INTERNATIONAL   CHEMICAL   SERIES 
H.  P.  TALBOT,  PH.D.,  CONSULTING  EDITOR 


THE 

CHEMICAL  AND  METALLOGRAPHIC 

EXAMINATION  OF 
IRON,  STEEL  AND  BRASS 


"Ms  Qraw-MlRook  &.  1m 


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THE 

CHEMICAL  AND  METALLOGKAPHIC 

EXAMINATION  OF 
IKON,  STEEL  AND  BRASS 


BY 

WILLIAM  T.  HALL 
M 

ASSOCIATE    PROFK8SOK    OP   ANALYTICAL  CHEMISTRT, 
MASSACHUSETTS   INSTITUTE    OF   TECHNOLOGY 


AND 
ROBERT  S.  WILLIAMS 

ASSOCIATE    PROFESSOR   OF  ANALYTICAL  CHEMISTRY  AND   METALLOGRAPHY, 
MASSACHUSETTS   INSTITUTE   OF  TECHNOLOGY 


FIRST  EDITION 


McGRAW-HILL  BOOK  COMPANY,  INC. 
NEW  YORK:  370  SEVENTH  AVENUE 

LONDON  :  6  &  8  BOUVERIE  ST.,  E.  C.  4 
1921 


COPYRIGHT,  1921,  BY  THE 
McGRAw-HiLL  BOOK  COMPANY,  INC. 


THE    JM  A   1>  1,  i;    PRBSS    YORK  PA 


PREFACE 

The  necessity  for  the  chemical  analysis  of  alloys  has  long  been 
recognized  but  modern  methods  of  manufacture  and  the  use  of 
metals  under  conditions  of  severe  strain  demand  additional 
information  which  can  best  be  obtained  by  the  examination  of 
polished  specimens.  Both  of  these  branches  of  metal  inspection 
are  considered  in  this  book. 

Part  I  deals  with  the  Chemical  Analysis  of  Alloys  and  includes 
well  tested  methods  of  analysis  selected  mainly  from  reports  of  the 
United  States  Bureau  of  Standards  or  from  papers  of  the  Ameri- 
can Society  for  Testing  Materials.  Although  most  of  the 
standard  methods  of  steel  analysis  are  included,  special  emphasis 
has  been  placed  on  those  methods  which  are  both  rapid  and 
accurate. 

Part  II  considers  the  physical  rather  than  the  chemical  in- 
spection of  metals  and  describes  the  methods  of  preparation 
and  examination  of  polished  metal  surfaces  as  an  independent 
means  of  determining  the  quality  of  material  as  well  as  an  aid  in 
getting  representative  samples  for  chemical  analysis.  A  brief 
introduction  to  metallography,  in  so  far  as  it  applies  to  the 
inspection  of  alloys,  is  included. 

The  authors  wish  to  express  their  sincere  appreciation  to 
Messrs.  Bauer  and  Deiss  whose  book  on  the  ''Sampling  and 
Analysis  of  Iron  and  Steel,"  translated  by  them  in  1915  and 
published  with  many  additions  and  modifications  suggested 
the  idea  of  combining  chemical  and  metallographic  inspection. 
A  small  portion  of  the  translation  is  included  in  this  book,  notably 
several  tables  and  a  number  of  photomicrographs  for  which  the 
authors  again  express  their  thanks. 

Grateful  acknowledgement  is  made  to  Professor  Henry  Fay 
for  the  use  of  several  photomicrographs  and  to  Dr.  W.  P.  Davey 
for  an  X-ray  Photograph.  Special  thanks  are  due  to  Mr.  V.  O. 
Homerberg  who  prepared  and  photographed  many  of  the  speci- 
mens used  in  illustration.  WILLIAM  T.  HALL 

ROBERT  S.  WILLIAMS. 

MASSACHUSETTS  INSTITUTE  OF  TECHNOLOGY, 
August,  1921. 

45G096 


CONTENTS 


PAGE 

PREFACE.  v 


PART  I. 

The  Chemical  Analysis  of  Iron,  Steel  and  Brass 

CHAPTER  I 
INTRODUCTION 3 

CHAPTER  II 
CARBON 7 

1.  Determination  of  Carbon  by  Direct  Combustion  in  Oxygen    .    .      11 

2.  Direct  Combustion  of  Carbon  in  Oxygen — Rapid  Method  ...      19 

3.  Combustion  of   Carbon  in  the  Wet  Way,   Corleis  Chrome — 

Sulfuric  Acid  Method 23 

4.  Determination    of    Total    Carbon    by    the    Potassium-Cupric- 

Chloride  Method 32 

5.  Determination  of  Carbon  by  the  Deiss  Method 37 

Determination  of  Graphite  and  Temper  Carbon 44 

Colorimetric  Method  for  Carbon  in  Steel 46 

CHAPTER  III 

MANGANESE 47 

1.  Determination  of  Manganese  by  the  Bismuthate  Method    ...  49 

2.  Determination  of  Manganese  by  the  Ford- Williams  Method  .    .  56 

3.  Determination  of  Manganese  by  the  Volhard  Method      ....  59 

4.  Determination  of  Manganese  by  the  Persulfate  Method  ....  69 

5.  Gravimetric  Determination  of  Manganese 70 

CHAPTER  IV 
PHOSPHORUS 90 

1.  Determination    of    Phosphorus    in    Steel    by    the    Malybdate- 

Magnesia  Method 91 

2.  Determination    of    Phosphorus    in    Steel    by    the    Alkalimetric 

Method 94 

3.  Determination  of  Phosphorus  in  Cast  Iron 96 

4.  Determination  of  Phosphorus  by  the  Johnson  Method 100 

5.  Determination  of  Phosphorus  by  the  Acetate  Method  of  A.  A. 

Blair  (Modified) 101 


Vlll  CONTENTS 

PAGE 

6.  Determination  of  Phosphorus  by  the  Permanganate  Titration    .  104 

7.  Determination  of  Phosphorus  in  Materials  Insoluble  in  Nitric 

Acid .109 

8.  Determination  of  Phosphorus  in  Materials  Containing  Arsenic   .  110 

9.  Determination  of  Phosphorus  in  Materials  Containing  Tungsten  111 
10.  Determination  of  Phosphorus  in   Materials  Containing  Vana- 
dium   113 

CHAPTER  V 

SILICON 115 

1.  Determination  of  Silicon  in  Materials  Soluble  in  Acid 115 

2.  Modified  Drown  Method , 119 

3.  Nitric  Acid  Method  for  Silicon  . 121 

4.  Determination  of  Silicon  in  Materials  Insoluble  in  Acid  ....  124 

CHAPTER  VI 

SULFUR 128 

1.  Determination  of  Sulfur  in  the  Presence  of  Iron 130 

2.  Bamber  Method  for  Determining  Sulfur  in  Iron  or  Steel      .    .    .  131 

3.  Determination  of  Sulfur  by  the  Ether  Method .131 

4.  lodometric  Determination  of  Sulfur  in  Steel 133 

5.  Determination  of  Sulfur  by  the  Simplified  Evolution  Method     .  135 

6.  Evolution    Method    and    Absorption    of    Hydrogen    Sulfide    in 

Bromine  and  Hydrochloric  Acid 137 

7.  Determination  of  Sulfur  in  Insoluble  Materials 141 

CHAPTER  VII 

COPPER • 142 

1.  Precipitation  as  Sulfide  from  Acid  Solution 142 

2.  Determination  of  Copper  after  Removal  of  Iron  with  Ether   .    .  144 

3.  Removal  of  the  Iron  with  Sulfuric  Acid 144 

4.  Electrolytic  Determination  of  Copper 145 

5.  The  Rapid  Determination  of  Copper  in  Steel 146 

CHAPTER  VIII 

CHROMIUM. 150 

1.  Determination     of     Chromium     by     the     Barium     Carbonate 

Method 150 

2.  Determination     of     Chromium     by    the     Method     of     Barba 

(Modified) 152 

3.  Determination  of  Chromium  by  the  Chlorate  Method      .    .    .    .153 

4.  Determination  of  Chromium  by  the  Bismuthate  Method     .    .    .154 

5.  Determination  of  Chromium  by  the  Ether  Method 155 

6.  Determination   of   Chromium   by    Fusion   of  the   Oxides   with 

Sodium  Peroxide 165 

7.  Determination  of  Chromium  in  Materials  Insoluble  in  Acid    .    .167 


CONTENTS  ix 

CHAPTER  IX 

PAGE 
IRON  .- 170 

1.  Determination  of  Iron  in  Materials  Soluble  in  Acid 

(A)  Mohr's  lodometric  Method 170 

(B)  Zimmermann-Reinhardt  Method 172 

2.  Determination  of  Iron  in  Insoluble  Materials 173 

CHAPTER  X 

NICKEL 175 

1.  Determination  of  Nickel  by  the  Dimethylglyoxime  Method    .    .    175 

2.  Determination  of  Nickel  by  Electrolytic  Deposition 178 

3.  Volumetric  Determination  of  Nickel  by  Potassium  Cyanide    .    .182 

4.  Determination  of  Nickel  by  the  Volumetric  Dimethylglyoxime 

Method 185 

5.  Determination   of   Nickel  by   Potassium   Cyanide  after   Ether 

Extraction 186 

CHAPTER  XI 
MOLYBDENUM 188 

1.  Determination  of  Molybdenum  by  the  Sodium  Peroxide  Fusion 

Method 190 

2.  Determination     of     Molybdenum    by    the     Ether     Extraction 

Method  of  Blair 192 

3.  Volumetric  Determination  of  Molybdenum 193 

CHAPTER  XII 
TUNGSTEN 195 

1.  Determination  of  Tungsten  as  Trioxide  by  Precipitation  from 

an  Acid  Solution  Containing  Cinchonine  Hydrochloride     ...    195 

2.  Determination  of  Tungsten  by  the  Deiss  Method 197 

3.  Determination   of   Tungsten   by   the    Sodium-Peroxide    Fusion 

Method 202 

4.  Determination  of  Tungsten  in  Materials  Insoluble  in  Acid  .    .    .   204 

CHAPTER  XIII 
VANADIUM 206 

1.  Determination  of  Vanadium  by  the  Phospho-Molybdate  Pre- 

cipitation Method 208 

2.  Determination  of  Vanadium  by  the  Blair  Method 210 

3.  Determination  of  Vanadium  by  an  lodometric  Method    .    .    .    .212 

4.  Determination  of  Vanadium  by  a  Fusion  Method 216 

5.  Gravimetric  Determination  of  Vanadium 217 


X  CONTENTS 

CHAPTER  XIV 

PAGK 

ALUMINIUM .    .  •. 220 

CHAPTER  XV 
ARSENIC 224 

CHAPTER  XVI 
COBALT R   •    •   227 

CHAPTER  XVII 
TITANIUM 231 

1.  Determination  of  Titanium  in  Materials  Soluble  in  Acid      .    .    .231 

(a)  Colorimetric  Determination 234 

(6)  Volumetric  Determination 236 

(c)  Determination  of  Iron  in  Impure  Titanium  Oxide    ....  238 

2.  Determination  of  Titanium  in  Insoluble  Materials.    .    .    .    ...  239 

CHAPTER  XVIII 
NITROGEN 243 

1.  Determination  of  Nitrogen  in  Steel  (Method  of  A.  H.  Allen)       .   243 

2.  Determination  of  Nitrogen  (Method  of  L.  E.  Barton) 246 

CHAPTER  XIX 

OXYGEN.    .........    ......  248 

1.  Ledebur's  Method  for  Oxygen 248 

2.  Method  of  Walker  and  Patrick  for  Determining  Oxygen  ....  252 

CHAPTER  XX 

ZIRCONIUM .....    ....    ........  258 

ALUMINIUM.  .    .    .    .    .    ;    ...    .    . .    ...    .    .  259 

(a)  In  the  Absence  of  Chromium 259 

(fe)  In  Steels  Containing  Chromium ".....  260 

(c)  In  Steels  Containing  Uranium .  260 

(d)  In  Steels  Containing  Vanadium .    .    .    ...  260 

DETERMINATION  OF  ZIRCONIUM  AND  TITANIUM  . 261 

CHAPTER  XXI 

ELECTROMETRIC  METHODS  APPLICABLE  TO  STEEL  ANALYSIS 264 

1.  Electro  metric  Determination  of  Chromium  in  Steel 280 

2.  Rapid  Method  for  Determining  Chromium  in  Steel 283 

3.  Determination  of  Manganese  by  the  Bismuthate  Method    .    .    .  285 

4.  Determination  of  Manganese  by  the  Persulfate  Method    .    .    .  287 

5.  Determination  of  Vanadium 288 

6.  Determination  of  Vanadium  and  Chromium  in  Fcrro  Vanadium  289 
THE  ELECTROMETRIC  DETERMINATION  OF  CARBON  IN  STEEL 295 


CONTENTS  xi 

CHAPTER  XXII 

PA  UK 

NON-FERROUS  ALLOYS 307 

Analysis  of  Aluminium  Bronze 310 

Analysis  of  Bearing  Metals 312 

Rapid  Volumetric  Analysis  of  Bearing  Metal.  . 315 

Determination  of  Arsenic  in  a  Copper  Alloy  ...........  318 

ANALYSIS  OF  BRASS  AND  BRONZE 319 

Tin .  .  . 321 

Tin  (Alternate  Method) .  .  .  .  .  ....  322 

Lead  and  Copper  (Method  A) .  7  .  ,  .  .'...'.'..  322 

Lead  and  Copper  (Method  B) ,  :.  .  .  ;  .  ....  ...  326 

Lead  and  Copper  (Method  C) .  ,  .  .  ./.  .  ...  327 

Iron ...  .  .  ..".  .. \  '.  ....  329 

Manganese 329 

Nickel :. ...  .  :.  .  .  .  .  .  .  :  .  .,  .  330 

Phosphorus 330 

Zinc .  /.  .....  -  331 

PART  II. 

The    Application    of    Metallography    to    the    Inspection    and 
Sampling  of  Alloys 

CHAPTER  XXIII 

PREPARATION  AND  EXAMINATION  OF  THE  SPECIMEN 337 

Polishing .    .    .  338 

Etching ....    .'  '.    .    .    .  341 

The  Microscope 342 

Photographing  the  Specimen 343 

CHAPTER  XXIV 

THE  METALLOGRAPHIC  CONSTITUENTS  OF  IRON  AND  STEEL 347 

The  Eutectic  Alloy 347 

The  Solid  Solution :..........-...  351 

The  Eutectoid -.,......  354 

The  Iron-Carbon  Diagram 356 

Etching  of  Steel  and  Iron 358 

Austenite 359 

Martensite 359 

Troostite 360 

Sorbite ;   ...  361 

Pearlite 361 

Ferrite 363 

Cementite 363 

Graphite  and  Graphitic  Temper  Carbon 364 


Xll  CONTENTS 

CHAPTER  XXV 

PAGE 

WROUGHT  IRON  AND  STEEL .  „  ..    . • ,.  • 367 

Cast  Steel 369 

Macroscopic  Examination  of  Steel 373 

Sulfur  Printing 378 

Direct  Prints  from  Etched  Steel 380 

Segregation '.......;.- 381 

CHAPTER  XXVI 

GENERAL  STUDY  OF  STEEL  WITH  THE  MICROSCOPE 390 

Tempering •    •   .• • 390 

Annealing  .........,./ 390 

Cold-worked  Material 392 

Case  Hardening 396 

Decarbonizing 396 

CHAPTER  XXVII 

METALLOGRAPHIC  EXAMINATION  OF  IRON .    . .  .    .    .   399 

Formation  of  Globules  and  Nodules 401 

Influence  of  Heat  on  White  Iron  (Malleabilizing)  .    .    ....    .    .    .   404 

CHAPTER  XXVIII 

GRAY  IRON ...    .    ...    .    ...    ....    .    .    .    .    .    .  410 

Effect  of  Cooling  Rate  on  Graphite .    .    .    .    .    .    .    .    ....    .    .    .  410 

Effect  of  Remelting  Gray  Iron ,    ~   .    . 418 

Effect  of  Annealing  on  Gray  Iron :  •    •    •    •    • 419 

Abnormal  Formations  in  Gray  Iron.    .    .    .  • 420 

CHAPTER  XXIX 

SAMPLING  OF  IRON  AND  STEEL  .....    .    .    .  ; .' 423 

General  Discussion  of  Sampling '. 423 

Sampling  of  Materials  Which  cannot  be  Machined  < 426 

Sampling  Wire 427 

Sampling  Molten  Metal 427 

Sampling  Forged  or  Rolled  Material . 428 

Sampling  Wrought  Iron 432 

Sampling  White  Iron 435 

Sampling  Gray  Iron. 436 

Sampling  in  Special  Cases 440 

Magnetic  Testing  of  Steel'.    . 441 

X-Rav  Examination  of  Steel.  . 443 


CONTENTS  xiii 

CHAPTER  XXX 

PAGE 

THE  ALLOYS  OF  COPPER 446 

Preparation  of  the  Specimens , 446 

Polishing 448 

Etching  of  Brass  and  Bronze 448 

Brass  and  Bronze 450 

The  Study  of  Worked  Material 458 

Annealing  of  Brass  and  Bronze 460 

Grain  Size.    .    , 464 

/3-Brass 468 

Season  Cracking 470 

Babbitt  Metal 474 

INDEX  481 


THE  CHEMICAL  AND  METALLO 

GRAPHIC  EXAMINATION  OF 

IRON,  STEEL  AND  BRASS 


PART  I 
THE  CHEMICAL  ANALYSIS 

OK 

IRON,  STEEL  AND  BRASS 


PART  I 

THE  CHEMICAL  ANALYSIS 

OF 

IRON,  STEEL  AND  BRASS 

CHAPTER  I 
INTRODUCTION 

The  importance  of  iron  and  steel  in  daily  life  has  led  to  the 
study  of  the  influence  of  every  chemical  element  likely  to  occur  in 
such  materials  either  as  intentional  ingredient  or  as  unintentional 
impurity.  This  study  has  involved  the  making  of  countless 
chemical  analyses  and  the  testing  of  many  methods.  The  pre- 
ponderance of  the  element  iron  influences  the  method  of  pro- 
cedure and  often,  when  only  small  quantities  of  certain  elements 
are  likely  to  be  present,  the  best  results  are  obtained  by  methods 
quite  unsuitable  for  the  exact  determination  of  large  quantities  of 
these  elements. 

The  elements  likely  to  be  found  in  ferrous  alloys  may  be  classi- 
fied into  three  groups  with  respect  to  the  frequency  with  which 
the  chemist  is  required  to  test  for  them.  The  first  group  includes 
the  elements  carbon,  manganese,  phosphorus,  silicon  and  sulfur. 
They  are  present  in  nearly  every  sample  of  iron  and  steel.  Both 
the  maker  and  user  are  interested  to  know  how  much  of  each  is 
present  and  often  the  material  is  valueless  for  certain  purposes 
unless  the  quantities  are  found  to  lie  within  fairly  narrow  limits. 
The  quantitative  determination  of  the  content  of  these  elements, 
therefore,  constitutes  the  regular  routine  work  of  every  chemist 
engaged  in  the  analysis  of  iron  and  steel.  The  actual  iron  con- 
tent of  commercial  iron  and  steel,  on  the  other  hand,  is  not 
usually  determined  by  direct  chemical  analysis  because  it  is 
easier,  and  in  many  cases  more  accurate,  to  assume  that  the 
element  iron  constitutes  the  remainder  of  the  metal.  The  above 
five  elements  are  quite  unlike  one  another  in  their  chemical 
characteristics.  They  will  be  discussed  in  alphabetical  order. 

3 


OF  METALS 


The  second  group  includes  the  elements  copper,  chromium, 
iron,  nickel,  molybdenum,  tungsten  and  vanadium.  Except 
iron,  these  elements  do  not  occur  to  an  appreciable  extent  in  most 
samples  of  iron  and  steel  but  they  are  important  constituents  of 
some  special  or  so-called  alloy  steels  and  it  is  important  thi- 
every chemist  should  know  how  to  detect  them  qualitatively  and 
to  determine  them  quantitatively.  When  the  iron  content  of 
the  metal  is  less  than  about  98  per  cent,  it  is  best  to  determine  the 
quantity  by  careful  chemical  analysis  as  it  is  not  always  safe  to 
assume  that  it  can  be  determined  "  by  difference."  The  chemical 
properties  of  the  first  four  members  of  this  group,  also  arranged 
in  alphabetical  sequence,  are  known  to  every  chemist.  The 
properties  of  the  last  three  elements  are  not  so  well  known  because 
they  are  not  always  discussed  fully  in  courses  of  chemical  instruc- 
tion given  at  our  colleges  and  technical  schools.  They  play  an 
important  part  in  modern  "  high-speed"  steels  so  that  they  can 
no  longer  be  regarded  as  rare  elements. 

The  third  group  includes  aluminium,  arsenic,  cobalt,  titanium 
nitrogen  and  oxygen.  These  elements  are  likely  to  occur  in  iron 
and  steel  and  many  authorities  feel  that  they  influence  the 
properties  of  the  metal  to  a  marked  degree.  The  quantities 
present  are  usually  small  and  there  is  often  considerable  difficulty 
in  making  the  analysis  with  satisfactory  accuracy.  It  is  known, 
for  example,  that  the  presence  of  oxides  is  likely  to  cause  the 
development  of  flaws  in  steel  but  it  is  usually  easier  to  detect 
oxide  inclusions  by  microscopic  examination  than  by  chemical 
analysis.  The  average  oxygen  content  of  the  metal  may  be  low 
but  at  one  particular  place  there  may  be  enough  slag  to  cause 
trouble. 

The  methods  to  be  described  for  the  analysis  of  iron  and  steel 
will  be  discussed  according  to  the  above  grouping.  In  most 
cases  a  number  of  methods  will  be  given,  all  of  which  have 
proved  capable  of  yielding  accurate  results.  Next,  will  follow 
a  chapter  on  electrometric  methods  for  analyzing  steel.  These 
methods  are  grouped  separately  partly  because  special  equipment 
and  different  technique  are  required  and  partly  because  it  is 
too  soon  to  predict  to  what  extent  they  will  replace  the 
better  known  methods  of  quantitative  analysis.  Finally,  a 
chapter  will  be  added  describing  methods  of  analysis  of  important 


INTRODUCTION  5 

commercial  alloys,  such  as  brass  and  bronze,  in  which  iron  is  not 
usually  an  intentional  constituent  and  which  are  known  as 
"  non-ferrous  "  alloys. 

So  many  good  methods  are  known  for  the  analysis  of  iron  and 
ceel  that  it  is  difficult  to  say  which  method  is  best.  According 
to  the  general  custom  in  text  books  on  analytical  chemistry,  it 
would  seem  natural  to  discuss  gravimetric  methods  first,  then 
volumetric  or  titration  methods  and  finally  electrolytic,  colori- 
metric  or  other  special  methods.  The  objection  to  this 
treatment  lies  in  the  fact  that  emphasis  is  likely  to  be  placed 
upon  methods  which  are  seldom  used  in  practice.  The  chemical 
balance  is  the  basis  of  all  exact  chemical  measurement  and,  for 
this  reason,  it  is  usually  assumed  that  the  most  accurate  methods 
are  those  in  which  the  final  result  is  obtained  by  weighing  some 
pure  compound.  For  determining  small  quantities  of  substances, 
however,  it  is  often  far  more  accurate  to  obtain  the  final  result 
by  titration  or  by  comparing  a  color  with  certain  standards. 
By  this  means  the  presence  of  quantities  which  cannot  be 
weighed  on  an  ordinary  chemical  balance  can  be  detected  and 
determined  with  precision.  An  attempt  will  be  made,  to  classify 
the  methods  with  respect  to  their  usefulness.  This  appears  very 
simple  on  the  surface  and  it  would  be  were  it  true,  as  chemists 
sometimes  assume,  that  there  is  always  one  best  method  for 
making  each  analysis.  An  experience  of  over  20  years  in  inspect- 
ing the  results  of  young  chemists  has  shown  that  there  is  individ- 
ual taste  in  chemistry  as  in  other  things.  Chemists  like  and 
dislike  chemical  methods  with  the  same  freedom  of  impulse  that 
they  show  in  liking  and  in  disliking  people.  Some  chemists  are 
able  to  get  good  results  by  methods  which  do  not  find  favor  with 
others.  Again,  a  relatively  inexperienced  person  may  become 
very  expert  in  making  a  certain  kind  of  chemical  analysis  and  yet 
his  judgment  with  regard  to  the  relative  values  of  methods  may 
be  faulty.  Often  the  reason  a  chemist  dislikes  a  certain  method 
is  due  to  a  slight  misunderstanding  of  some  particular  point. 

Probably  no  two  chemists  would  agree  absolutely  with  respect 
to  the  relative  reliabilities  of  the  various  methods  to  be  described. 
In  many  cases  the  choice  will  vary  with  respect  to  the  nature  of 
the  material  examined.  In  Germany,  the  Volhard  method 
appears  to  be  the  favorite  one  for  the  determination  of  manganese 


6  CHEMICAL  ANALYSIS  OF  METALS 

in  iron  and  steel,  in  this  country  A.  A.  Blair  and  others  have  advo- 
cated the  use  of  the  "  bismuthate  "  method  while  in  many  other 
laboratories  the  "persulfate"  method  is  preferred  for  determining 
small  quantities  of  manganese  and  the  Volhard  method  is  used 
for  larger  quantities.  Again,  in  the  case  of  carbon,  it  is  possible 
to  get  excellent  results  by  a  variety  of  procedures.  In  Germany 
the  Corleis  chrome-sulfuric  acid  method  is  well-liked  but  equally 
good  results  can  be  obtained  in  a  fraction  of  the  time  by  means 
of  direct  combustion  in  the  electric  furnace.  In  deciding  upon 
the  relative  usefulness  of  methods,  due  respect  will  be  paid  to  the 
recommendations  of  the  American  Society,  for  Testing  Materials 
and  to  the  work  done  by  the  Bureau  of  Standards  at  Washington, 
D.  C.  It  should  be  borne  in  mind,  however,  that  all  chemists 
and  all  methods  are  fallible,  and  it  is  just  as  desirable  to  check  up 
results  in  doubtful  cases  by  different  methods  as  it  is  to  have  the 
work  checked  by  another  chemist.  It  is  one  of  the  most  dis- 
couraging happenings  in  the  life  of  a  chemist  to  have  something 
go  wrong  for  an  unsuspected  reason.  Sometimes  the  trouble  is 
caused  by  impure  reagents,  sometimes  by  the  presence  of 
an  unsuspected  element  and  sometimes  by  a  slight  error  in 
manipulation. 

This  book  is  written  more  from  the  point  of  view  of  the  educa- 
tor than  from  that  of  the  busy  analyst.  A  person  who  can  blindly 
follow  directions  in  the  laboratory  without  understanding  the 
nature  of  the  chemical  reactions  involved  is  not  a  chemist  any 
more  than  is  the  housewife  who  follows  the  directions  of  the 
cook  book  and  gets  good  results  in  the  chemical  reactions  of 
cooking.  In  the  long  run,  the  chemical  worker  becomes  more 
efficient  and  more  reliable  when  he  knows  what  he  is  doing  and 
why  he  is  doing  it.  To  be  sure,  the  man  who  knows  less  is 
sometimes  willing  to  work  for  less  and  for  this  reason  employers 
are  often  willing  to  employ  ignorant  labor.  Sometimes  such 
persons  do  very  conscientious  work  in  the  chemical  laboratory 
and  obtain  excellent  results.  It  is  easier  to  teach  a  man  to 
weigh  and  to  read  a  burette  than  it  is  to  make  a  scholar.  This 
book  is  not  written  for  the  chemical  laborer  so  much  as  for  the 
man  who  wants  to  know  and  to  understand  methods  of  chemical 
analysis. 


CHAPTER  II 
CARBON 

Carbon  occurs  in  iron  and  steel  in  the  combined  form  as 
carbide,  as  a  solid  solution  of  iron  carbide  in  iron,  and  in  the 
uncombined  state  as  graphite  or  as  temper  carbon. 

Absolutely  reliable  methods  for  the  determination  of  combined 
carbon  in  the  presence  of  free  carbon  are  not  known  but  it  is 
possible  to  determine  the  total  carbon  and  that  which  is  uncom- 
bined. In  order,  therefore,  to  determine  the  amount  of  com- 
bined carbon  in  a  sample,  the  total  carbon  and  free  carbon  are 
determined  separately  and  the  combined  carbon  found  by 
difference. 

Graphite  and  temper  carbon  cannot  be  separated  by  chemical 
means.  It  is  possible  in  many  cases,  by  means  of  the  metallo- 
graphic  method  described  in  the  Part  II  of  this  book,  to  find  out 
whether  the  free  carbon  is  present  as  graphite  or  as  temper 
carbon. 

Iron  carbide,  Fe3C,  is  often  called  cementite.  It  occurs  in  all 
annealed  steels  and  in  irons  which  have  been  chilled  in  passing 
from  the  liquid  to  the  solid  state  (white  cast  iron).  The  eutec- 
toid  mixture  of  cementite  and  free  iron  is  called  pearlite.  Pearlite 
contains  approximately  0.85  per  cent  C  and  steels  with  less  car- 
bon are  called  hypo-eutectoid  and  with  higher  carbon  they  are 
hyper-eutectoid.  When  quenched  above  the  critical  temperature, 
the  iron  carbide  remains  dissolved  in  solid  iron  and  the  solid 
solution  according  to  its  nature  and  appearance,  is  known  as 
austenite,  martensite,  troostite,  or  sorbite.  These  represent  dif- 
ferent conditions  of  the  solid  solution.  In  cast  irons  at  the 
temperature  of  about  1,000°C.,  and  particularly  when  the 
silicon  content  is  high,  the  iron  carbide  breaks  down  into  iron 
and  graphite  (gray  cast  iron).  Temper  carbon  is  formed  by 
heating  irons  rich  in  cementite  to  about  1,000°  in  the  production 
of  malleable  cast  iron.  It  is  sometimes  found  in  annealed, 

7 


CHEMICAL  ANALYSIS  OF  METALS 

high-carbon  steel.     The  structure  of  iron  and  steel  is  discussed 
more  fully  in  Part  II. 

Graphite  and  temper  carbon  are  not  affected  by  boiling,  dilute 
mineral  acids.  Hot,  concentrated  nitric  acid  has  a  slow  oxidizing 
effect  upon  them,  the  graphite  flakes  being  harder  to  attack  than 
the  temper  carbon.  The  latter  also  burns  more  readily  in  oxygen. 

Dilute  hydrochloric  or  sulfuric  acid  decomposes  iron  carbide 
with  the  evolution  of  more  or  less  hydrocarbon  so  that  the 
hydrogen  evolved  on  treating  iron  or  steel  with  these  acids  is 
always  contaminated  with  hydrocarbons.  When  a  sample  of 
steel  is  treated  with  cold,  dilute  nitric  acid,  the  iron  dissolves 
and  the  iron  carbide  is  left  behind  as  a  brown  flocculent  residue 
which  goes  into  solution  at  about  80°,  giving  a  dark  color  to  the 
solution  which  is  roughly  proportional  to  the  carbide  content 
of  the  steel.  (Colorimetric  Method,  often  used  in  routine  work.) 
The  iron  carbide  held  in  solid  solution  by  the  iron,  or,  in  other 
words,  that  present  as  austenite,  martensite,  and  even  in  troostite 
or  sorbite  which  many  consider  as  colloidal  solutions,  is  somewhat 
more  soluble  in  nitric  acid  than  the  free  cementite.  It  can  be 
distinguished,  roughly,  from  free  cementite  by  the  fact  that  it 
will  dissolve  in  dilute  nitric  acid  upon  shaking  at  ordinary  tem- 
peratures. It  also  imparts  a  brown  color  to  the  nitric  acid  solu- 
tion and  the  color  is  not  quite  identical  with  that  produced  by  the 
same  percentage  of  carbon  present  as  free  cementite  in  the 
metal. 

Besides  iron  carbide,  Fe3C,  carbides  of  manganese,  chromium, 
tungsten,  molybdenum  and  vanadium  are  also  found  in  certain 
steels. 

DETERMINATION  OF  TOTAL  CARBON 

Experts  in  metallographic  work  can  often  estimate  the  carbon 
content  of  fully-annealed  steel  fairly  closely  by  microscopic 
examination.  All  accurate  chemical  methods  for  determining 
the  total  carbon  content  of  a  metal  depend  upon  the  oxidation 
of  the  carbon  to  carbon  dioxide.  This  oxidation  may  be  accom- 
plished by  heating  in  a  furnace  in  a  stream  of  oxygen  or  it  may  be 
effected  in  the  wet  way  by  treating  with  acid  and  a  very  strong 
oxidizing  solution.  When  the  combustion  takes  place  in  the 
furnace,  it  was  for  a  long  time  considered  advisable  to  remove 
most  of  the  iron  first.  Thus  Wohler  (1869),  heated  the  metal 


CARBON  9 

in  a  stream  of  pure  chlorine  gas  whereby  iron,  silicon,  phos- 
phorus, sulfur,  and  certain  other  elements  that  are  occasionally 
present,  were  converted  into  volatile  chlorides  leaving  behind 
all  the  carbon  and  a  small  quantity  of  non- volatile  chloride.  The 
silicon  present  in  the  slag  is  also  unaffected  by  this  treatment. 
Berzelius  recommended  dissolving  out  the  iron  by  means  of  a 
solution  containing  cupric  and  ammonium  chlorides  and  Richter 
replaced  the  ammonium  chloride  with  potassium  chloride  because 
the  former  is  likely  to  contain  a  little  pyridine  chloride.  For 
years  this  double  salt,  2KCl.CuCl2.2H2O,  often  called  in  steel 
laboratories  the  double  chloride,  was  general^  used  for  the  pre- 
liminary treatment  of  iron  and  steel  when  the  total  carbon  was 
to  be  found  by  dry  combustion.  Experience  showed  that  it 
was  desirable  to  have  some  free  hydrochloric  acid  present. 

This  preliminary  treatment  with  double  chloride  requires  con- 
siderable time  and  for  that  reason,  probably,  the  wet  combustion 
method  became  popular,  particularly  in  Europe.  With  the 
advent  of  the  electric  furnace,  however,  and  the  more  accurate 
study  of  the  temperature  necessary  to  accomplish  complete 
combustion,  it  was  soon  found  that  carbon  determinations  with 
the  highest  possible  degree  of  accuracy  can  be  accomplished  by 
direct  combustion,  i.e.  by  heating  the  original  sample  of  metal  in 
oxygen  without  any  preliminary  treatment  except  that  of  get- 
ting it  into  sufficiently  small-sized  particles.  It  is  difficult  to 
oxidize  completely  a  very  large  lump  of  metal  but  it  is  not 
necessary,  or  even  desirable  to  reduce  the  material  to  the  size 
of  coarse-grain  powder. 

After  the  solid  carbon  has  been  oxidized  to  gaseous  carbon 
dioxide,  the  next  step  is  to  absorb  the  gas  by  some  suitable 
alkaline  reagent.  Potassium  hydroxide  solution,  solid  soda- 
lime,  asbestos  impregnated  with  sodium  hydroxide  and  barium 
hydroxide  solution  are  the  common  absorbents  used.  Sodium 
hydroxide  solution  is  not  as  satisfactory  as  potassium  hydroxide 
solution  because  of  the  insolubility  of  sodium  bicarbonate.  As 
regards  the  relative  advantages  of  the  above  four  reagents  as 
absorbents  for  carbon  dioxide  gas,  opinions  differ.  Certainly 
soda-lime,  when  in  the  proper  condition,  is  as  good  as  any  but 
there  are  three  disadvantages  arising  from  its  use.  (1)  It  is 
not  always  easy  to  tell  from  the  appearance  of  the  reagent 


10  CHEMICAL  ANALYSTS  OF  METALS 

whether  it  is  in  the  proper  physical  and  chemical  condition. 
Sometimes  the  sample  as  purchased  is  practically  worthless  for 
exact  quantitative  work.  (2)  It  does  not  of  itself  give  any 
indication  of  the  rate  at  which  the  gas  is  passing  through  the  tube 
containing  it.  Sometimes  the  combustion  tube  will  crack  and 
nearly  all  of  the  gas  escape  without  the  operator  being  aware 
of  the  fact.  (3)  To  tell  whether  the  first  soda-lime  is  absorbing 
all  of  the  carbon  dioxide  it  is  necessary  to  use  at  least  two  weighed 
tubes.  The  tubes  are  used  repeatedly  until  a  gain  in  weight  is 
noticed  in  the  second  tube,  when  the  first  tube  is  refilled  and 
used  as  the  second  tube.  This  necessitates  the  weighing  of  two 
tubes  before  and  after  each  combustion.  Many  of  these  objec- 
tions to  the  use  of  soda-lime  are  overcome  by  the  use  of  asbestos 
impregnated  with  solid  sodium  hydroxide  as  described  in 
Method  2.  Caustic  potash  solution  in  a  suitable  absorption  bulb, 
usually  of  the  type  recommended  by  Geissler,  can  be  used  re- 
peatedly until  a  precipitate  of  potassium  bicarbonate  appears  and 
a  satisfactory  absorption  can  be  accomplished  with  one  bulb  if  the 
flow  of  gas  is  not  too  rapid.  Absorption  in  a  Geissler  bulb  is  not 
satisfactory  when  the  combustion  is  conducted  rapidly,  as  in 
some  of  the  modern  laboratories,  because  the  absorption  may  be 
incomplete  and  some  of  the  water  from  the  solution  may  be 
swept  pass  the  drying  agent  at  the  end  of  the  bulb. 

When  soda-lime  or  potassium  hydroxide  solution  is  used  as 
absorbent,  the  carbon  content  of  the  original  metal  is  computed 
from  the  gain  in  weight  produced  by  the  absorbed  carbon 
dioxide.  With  barium  hydroxide,  there  are  four  other  methods 
of  arriving  at  the  same  result.  (1)  The  precipitated  barium 
carbonate  may  be  filtered  off,  heated  in  a  crucible  and  weighed. 

(2)  A  definite  volume  of  barium  hydroxide  of  known  concentra- 
tion may  be  used  as  absorbent  and  subsequently  the  loss  in 
alkalinity  due  to  formation  of  barium  carbonate  determined  by 
titrating  with  dilute  acid  using  phenolphthalein  as  indicator. 

(3)  The  barium  carbonate  may  be  filtered  off  and  analyzed  by 
titration  with   dilute   acid,   using  methyl  orange   as  indicator. 

(4)  The  barium  hydroxide  content  of  a  measured  quantity  of  the 
solution  may  be  determined  before  and  after  the  combustion  by 
measuring  the  electrical  resistance  of  the  solution.     This  last 
method  will  be  described  in  Chap.  XIX. 


CARBON  11 

1.  DETERMINATION  OF  CARBON  BY  DIRECT  COMBUSTION 
IN  OXYGEN 

METHOD  OF  J.  R.  CAIN  AND  L.  C.  MAXWELL* 

Principle. — The  carbon  dioxide  obtained  by  direct  combustion 
is  absorbed  by  barium  hydroxide  solution;  the  precipitated 
barium  carbonate  is  filtered  off,  dissolved  in  a  measured  quantity 
of  standard  hydrochloric  acid  and  the  excess  of  the  latter  titratecf 
with  standard  alkali,  using  methyl  orange,  as  indicator. 

The  use  of  barium  hydroxide  as  absorbent  was  suggested  by 
Pettenkofer2  for  the  analysis  of  air  and  the  practice  has  been 
applied  to  the  determination  of  carbon  in  iron  and  steel.3  For  a 
long  time,  however,  the  method  received  little  attention  in  the 
standard  text  books  on  iron  and  steel  analysis.  In  1913  about 
40  per  cent  of  the  prominent  American  laboratories  used  barium 
hydroxide  but  in  most  cases  the  resulting  barium  carbonate 
was  weighed. 

Apparatus. — Furnace. — Any  apparatus  may  be  used,  whether 
heated  by  gas  or  electricity,  which  will  permit  heating  the  sample 
in  oxygen  at  about  1,100°C.  Thus  the  various  forms  of  tubulated 
platinum  crucibles  are  suitable  but  expensive.4  An  electric 
furnace  of  the  resistance  type  is  recommended. 

Such  a  furnace  can  be  purchased  or  it  may  be  made  by  winding 
an  alundum  core  with  nichrome  wire  and  surrounding  it  with 
sufficient  insulating  material  to  prevent  loss  of  heat.  The  fur- 
nace should  be  8  to  12  in.  long  and  capable  of  holding  a  combus- 
tion tube  about  1.5  in.  in  diameter.  It  should  be  capable  of 
operating  continuously  at  not  less  than  1,063°  (m.p.  of  pure  gold). 
The  furnace  should  be  equipped  with  a  rheostat  so  designed  with 
respect  to  the  line  voltage  that  the  proper  temperature  will  be 
obtained  with  nearly  all  the  rheostat  resistance  inserted.  As  the 
furnace  is  used,  the  nichrome  windings  deteriorate  and  the  resist- 

1  Bureau  of  Standards,  Technologic  Paper  No.  33.  Am.  Soc.  Testing 
Materials,  1915,  201.  CAIN  and  MAXWELL,  /.  7.  E.  C.,  10,  520  (1918); 
11,  852  (1919). 

2/.  pr.  Chem.,  82,  32  (1861). 

3  PETTERSON  and  SMITH,  Ber.  23  (1401);  Z.  Anal.  Chem.,  32,  385.     AUP- 
PERLE,  /.  Am.  Chem.  Soc.,  28,  858.     MCFARLANE  and  GREGORY,  Chem. 
News,  94,  133. 

4  cf.  SHIMER,  P.  W.,  /.  7.  E.  C.,  1,  738  (1909). 


12  CHEMICAL  ANALYSIS  OF  METALS 

ance  of  the  furnace  increases  so  that  more  current  must  be  used. 
To  avoid  overloading  the  furnace  it  is  best  to  have  an  ammeter  in 
the  circuit;  with  the  110-volt  circuit,  about  4  amperes  should  be 
sufficient  for  running  the  furnace. 

The  furnace  may  be  used  with  a  standard  thermo-couple  or 
may  be  calibrated  with  the  aid  of  a  thermo-couple  so  that  the 
operator  can  judge  the  approximate  temperature  by  the  ammeter 
reading.  The  simplest  method  to  check  the  temperature  of  the 
furnace  is  by  means  of  the  melting  point  of  pure  gold.  Flatten 
out  a  piece  of  this  metal,  place  it  on  a  clean  porcelain  or  alundum 
boat  and  leave  it  in  the  hot  furnace  for  10  min.  If  the  gold  does 
not  melt,  the  temperature  is  low.  The  same  piece  of  gold  may 
be  used  repeatedly  if  it  is  placed  on  a  clean  surface  of  porcelain 
or  alundum  each  time. 

Combustion  Tubes. — With  the  electric  furnace,  the  combustion 
itself  takes  place  in  a  tube  about  24  in.  long  and  1  in.  in  diameter. 
The  tube  may  be  made  of  quartz  or  porcelain,  glazed  on  one  or 
both  sides.  Quartz  sometimes  becomes  de vitrified  and  porous 
when  used  continuously.  Platinum  tubes  are  good  but  the  cost 
is  prohibitive.  To  protect  the  tube  from  spattered  oxides,  a 
sleeve  of  sheet  nickel  (ignited  till  free  from  carbon)  should  be 
provided.  This  should  be  longer  than  the  combustion  boat  and 
be  placed  in  the  center  of  the  tube. 

Catalyzer. — In  the  front  end1  of  the  combustion  tube,  place  a 
roll  of  copper  gauze  about  3  in.  long  and  large  enough  to  fill  the 
tube.  It  should  not  be  placed  far  enough  into  the  furnace  so 
that  there  is  danger  of  its  melting.  It  should  be  heated  to 
about  250°.  On  heating  in  oxygen,  the  copper  becomes  changed 
to  cupric  oxide,  CuO,  which  serves  as  a  catalyzer  to  insure  the 
complete  combustion  of  the  carbon  and  it  also  acts  as  a  retainer 
of  any  sulfuric  acid  that  may  be  formed  from  the  sulfur  of  the 
iron  or  steel.  If  much  copper  sulfate  accumulates  in  the  tube, 
the  catalyzer  should  be  renewed. 

Instead  of  copper  oxide,  platinized  quartz  or  asbestos  may  be 
used.  Deiss  recommends  placing  a  loose  plug  of  ignited  asbestos 

1  The  various  parts  of  the  apparatus  when  united  form  a  train.  The  flow 
of  the  gas  is  assumed  to  take  place  from  back  to  front  and  the  front,  or 
foward  end,  is  where  the  gas  leaves  the  train.  In  most  drawings,  the  front 
end  is  shown  on  the  right. 


CARBON  13 

in  the  tube  at  the  front  end  of  the  furnace,  and  in  front  of  the 
plug  in  the  projecting  tube  he  uses  a  2-in.  layer  of  copper  oxide 
and  an  equally  long  layer  of  a  mixture  of  9  parts  potassium 
chromate  and  1  part  of  potassium  dichromate  which  has  been 
previously  melted  in  a  porcelain  crucible  and  then  reduced  to 
coarse  powder.  Fay1  recommends  as  catalyzer  a  2-in.  roll  of 
ignited  asbestos  wrapped  in  nickel  gauze.  A  similar  roll  placed 
in  the  back  of  the  furnace  helps  to  protect  the  rubber  stoppers 
from  radiated  heat.  To  decrease  the  dead  space  in  the  furnace, 
it  is  well  to  place  a  piece  of  large  glass  rod  in  front  of  the  catalyzer. 

Boats. — The  iron  or  steel  sample  to  be  analyzed  is  placed  on  an 
open  vessel  called  a  combustion  boat.  Suitable  boats  made  of 
porcelain,  quartz,  alundum,  clay  or  platinum  may  be  purchased. 
Nickel  boats  may  be  made  by  cutting  a  piece  of  sheet  nickel  at 
the  corners  and  bending  these  up.  Such  boats  are  inexpensive. 
To  protect  the  boat  from  the  action  of  melted  iron  oxide,  a  little 
alundum  sand  is  placed  in  it  as  lining  and  the  iron  or  steel  placed 
on  the  alundum. 

Absorption  Tube. — A  Meyer  tube  having  8  or  10  bulbs,  each  of 
10  or  15  c.c.  capacity,  is  recommended.  When  such  a  tube  is 
filled  with  barium  hydroxide  solution,  the  absorption  of  the 
carbon  dioxide  takes  place  satisfactorily  even  when  the  gas  is 
passing  through  quite  rapidly.  In  front  of  the  Meyer  bulb  it  is 
best  to  place  a  soda-lime  tube  to  protect  the  barium  hydroxide 
from  the  carbon  dioxide  in  the  atmosphere. 

Purification  Train. — This  method  eliminates  the  necessity  of  a 
purifying  train  in  front  of  the  furnace  as  no  precautions  are 
necessary  to  prevent  moisture  or  sulfur  trioxide  getting  into  the 
barium  hydroxide  solution.  With  oxygen  of  good  quality  it  is 
not  necessary  to  have  the  gas  purified  before  it  enters  the  furnace. 
Sometimes,  however,  there  is  a  little  organic  matter  in  the  oxygen. 
To  remove  this,  pass  the  gas  through  a  12-in.  porcelain  tube 
containing  granular  copper  oxide  and  heated  to  about  900°. 
In  front  of  this  tube  place  a  soda  tower  filled  with  soda-lime  or 
stick  caustic  soda. 

Solutions  Required. — Tenth-normal  Hydrochloric  Acid. — Use 
8  c.c.  of  concentrated  hydrochloric  acid  (d.  1.1  =  approxi- 
mately 12-normal)  per  liter.  After  thoroughly  mixing  the  diluted 

1  "An  Advanced  Course  in  Quantitative  Analysis,"  p.  60. 


14  CHEMICAL  ANALYSIS  OF  METALS 

acid,  standardize  it  against  pure  sodium  carbonate,  (Gay-Lussac) 
made  by  heating  pure  sodium  bicarbonate  at  270  to  300°  for 
J^  hr.  and  cooling  in  a  desiccator;  against  sodium  oxalate  (Soren- 
sen)  which  after  being  weighed  out  is  converted  into  sodium 
carbonate  by  carefully  heating  in  a  platinum  crucible  over  a 
small  flame  with  the  bottom  of  the  crucible  a  dull  red ;  or  by  the 
following  precipitation  method.  Carefully  measure  out  at  least 
20  c.c.  of  the  acid,  dilute  with  water  to  a  volume  of  50-60  c.c. 
and  add  a  slight  excess  of  approximately-tenth-normal  silver 
nitrate  solution.  Digest  at  70  to  90°  until  the  supernatant  liquid 
is  clear  and  then  filter  through  a  weighed  Gooch  crucible.  Wash 
the  precipitate  with  water  containing  2  per  cent  of  6-normal 
nitric  acid  until  a  portion  of  the  filtrate  shows  no  test  for  silver 
when  treated  with  a  drop  of  hydrochloric  acid.  Dry  to  constant 
weight  at  about  130°.  Duplicate  determinations  should  agree 
within  0.0005  g.  of  silver  chloride. 

Methyl  Orange. — Dissolve  0.02  g.  of  the  dyestuff  in  100  c.c.  of 
hot  water  and  filter  when  cold. 

Tenth-normal  Sodium  Hydroxide. — Dissolve  4  g.  of  pure  caustic 
soda  in  each  liter  of  solution.  When  methyl  orange  is  to  be  used 
as  indicator,  it  is  not  necessary  to  protect  the  sodium  hydroxide 
from  the  carbon  dioxide  of  the  atmosphere,  because  one  molecule 
of  sodium  carbonate  has  the  same  neutralizing  effect  as  one  mole- 
cule of  sodium  hydroxide.  Standardize  the  sodium  hydroxide  by 
titrating  portions  of  at  least  20  c.c.  against  the  hydrochloric  acid 
solution.  To  obtain  concordant  results  it  is  necessary  to  work 
with  a  small  quantity  of  methyl  orange  (about  1  drop)  and  always 
at  about  the  same  dilution.  Moreover,  it  is  best  to  match  the 
color  of  the  end-point  with  that  produced  by  adding  less  than  1 
drop  of  the  acid  to  the  same  volume  of  distilled  water  as  that  of 
the  titrated  solution. 

Barium  Hydroxide  Solution. — Dissolve  25  g.  of  barium  hydrox- 
ide, Ba(OH)2.8H2O,  in  each  liter  of  water.  Allow  the  well- 
mixed  solution  to  stand  2  days  and  then  siphon  off  the  clear 
liquid  through  a  filter  into  a  large  stock  bottle.  The  bottle 
should  be  placed  on  a  shelf  and  be  provided  with  a  soda-lime  tube 
to  protect  it  from  the  carbon  dioxide  in  the  atmosphere.  (See 
Fig.  1.)  The  stopcock  on  the  siphon  tube  should  be  pro- 
tected by  a  rubber  stopper  when  not  in  use  so  that  it  will  not 


CARBON 


15 


Barium  — 


FlQ.  1. 


become  clogged  with  barium  carbonate.  Enough  barium  hy- 
droxide solution  should  be  used  in  the  analysis  so  that  each  small 
bulb  of  the  Meyer  tube  is  filled  and  half  of  the  larger  exit  bulb. 

After  setting  up  the  apparatus  it  must  be  tested  carefully  for 
leaks.  The  combustion  tube  should  next  be  heated  while  oxygen 
is  passed  through  it  to  destroy  all  organic  matter.  A  blank  run 
should  then  be  made  in  exactly  the  same 
way  as  in  the  analysis  of  a  weighed  sample 
and  the  final  titration  ought  not  to  show 
more  than  0.0001  g.  of  carbon. 

Procedure. — Place  a  layer  of  alundum 
sand  in  the  combustion  boat  and  give  it  a  Hydroxide 
preliminary  heating  in  the  furnace  before  Solution 
weighing  out  the  sample.  Then,  with  the 
furnace  at  the  proper  temperature  and  the 
filled  Meyer  tube  in  place,  withdraw  the 
boat  by  means  of  a  stout  wire  bent  to  form 
a  hook  and  allow  it  to  cool  until  its  temperature  is  just  below  a 
visible  red.  This  will  not  cause  loss  of  carbon  unless  the  particles 
of  metal  are  less  than  60-mesh  in  size.  Satisfactory  results 
are  obtained  with  chips  that  will  just  pass  through  a  10-mesh 
sieve.  Transfer  the  weighed  sample  to  the  boat,  quickly  push  it 
into  the  proper  place  in  the  furnace  and  insert  the  stopper  at  the 
back  end  of  the  furnace.  With  metal  containing  about  1  per 
cent  of  carbon  or  less,  use  2  g.  of  samples  and  only  1  g.  if  the 
carbon  content  is  higher. 

Allow  the  sample  to  heat  for  1  min.  in  the  furnace  without 
passing  oxygen  into  the  tube.  (During  this  minute  a  second 
sample  of  steel  can  be  weighed  out.)  Then  begin  to  pass  oxygen 
into  the  tube  at  the  rate  of  300  to  400  c.c.  per  minute,  taking  care 
that  the  rate  of  flow  at  the  front  end  of  the  tube  is  not  greater 
than  225  c.c.  per  minute,  as  otherwise  the  absorption  of  the  carbon 
dioxide  will  be  incomplete.  The  combustion  of  2  g.  of  iron  re- 
quires approximately  600  c.c.  of  oxygen.  In  this  method  it  is 
desired  to  accomplish  complete  oxidation  of  the  sample  in  about 
2  min.  so  that  it  is  important  to  supply  the  oxygen  rapidly  at  the 
start.  The  gas  should  be  kept  bubbling  through  the  Meyer  bulb. 
The  rate  of  flow  at  the  front  end  of  the  furnace  should  never 
exceed  200  c.c.  per  minute.  By  placing  a  glass  capillary  tube  in 


16  CHEMICAL  ANALYSIS  OF  METALS 

the  rubber  stopper  at  the  front  end  of  the  furnace  the  escape  of 
gas  from  the  tube  is  hindered.  A  plug  of  glass  wool  should  be 
placed  back  of  the  capillary.  With  this  arrangement  the  flow 
of  gas  into  the  furnace  is  cut  down  automatically  as  soon  as  the 
combustion  of  the  sample  is  complete. 

At  the  end  of  5  min.  the  Meyer  tube  may  be  disconnected  and 
the  boat  allowed  to  cool  sufficiently  for  introducing  another 
sample. 

Pour  off  the  contents  of  the  Meyer  bulb  into  a  Btichner  funnel 
fitted  to  a  suction  flask  and  containing  two  7-  cm.  filter  papers, 
one  on  top  of  the  other.  Wash  out  the  tube  three  times  with 
distilled  water  that  has  been  boiled  to  remove  carbon  dioxide 
and  cooled  in  at  an  atmosphere  free  from  carbon  dioxide  (by 
causing  all  air  that  comes  in  contact  with  it  to  pass  through  a  soda- 
lime  tube).  Then  wash  the  filter  four  times,  taking  care  that 
the  top  of  the  funnel  is  washed  at  the  same  time. 

To  the  rinsed  Meyer  tube  add  from  a  burette  about  5  c.c.  more 
of  the  tenth-normal  hydrochloric  acid  than  is  necessary  to  dis- 
solve all  the  barium  carbonate.  Transfer  the  acid  from  the 
Meyer  tube  to  a  wide-mouthed  flask  into  which  also  place  the 
filter  papers  containing  a  part  of  the  precipitate.  Rinse  out  the 
Meyer  tube  with  two  portions  of  the  boiled  water.  It  may  then 
be  filled  with  fresh  barium  hydroxide  solution  and  is  ready  for 
another  determination.  Heat  the  flask  containing  the  acid  on 
the  hot  plate  until  all  of  the  barium  carbonate  has  dissolved. 
Avoid  long  heating,  however.  Titrations  are  conveniently  made 
when  several  flasks  are  ready. 

Cool  the  solution,  if  necessary,  and  titrate  with  standard 
sodium  hydroxide  with  methyl  orange  as  indicator. 

Computation.  —  One  liter  of  normal  acid,  or  alkali,  is  equivalent 
to  67.00  g.  of  pure  sodium  oxalate,  53.00  g.  of  pure  sodium  car- 
bonate or  143.3  g.  of  silver  chloride.  If  t  c.c.  of  hydrochloric 
acid  solution  were  found  in  the  standardization  to  be  equivalent 
to  a  g.  of  sodium  oxalate,  sodium  carbonate  or  silver  chloride, 
according  to  the  method  of  standardization,  then 


in  which  NA  represents  the  concentration  of  the  acid  in  terms 


CARBON  17 

of  a  normal  solution,  e  is  0.067  for  sodium  oxalate,  0.053  for 
sodium  carbonate  or  0.1433  for  silver  chloride,,  according  to 
the  method  of  standardization. 

If,  in  titrating  the  acid  against  the  base,  it  is  found  that  TI 
c.c.  of  acid  are  equivalent  to  r2  c.c.  of  the  base,  then  the  concen- 
tration of  the  sodium  hydroxide  in  terms  of  a  normal  solution  is 
shown  by  the  expression 


One  liter  of  normal  acid,  or  alkali,  is  equivalent  in  this  method 
to  6.00  g.  of  carbon,  or  1  c.c.  =  0.00600  g.  C.  If,  then,  HI  c.c.  of 
acid  and  n2  c.c.  of  base  are  used  in  the  titration  of  the  barium 
carbonate  precipitate  from  s  g.  of  material,  we  have 


Per  cent  C  = 


If  the  acid  and  alkali  are  both  exactly  tenth-normal,  and 
exactly  2  g.  of  metal  were  used  (accurate  to  within  0.01  g.)  then, 
using  the  above  notation, 

Per  cent  C  =  0.3  (m  -  n2) 

NOTES. — It  is  absolutely  essential  in  this  method  to  admit 
the  oxygen  very  fast  while  the  sample  is  burning  and  to  have  the 
temperature  of  the  furnace  near  1,100°C.  The  laboratory 
atmosphere  must  be  reasonably  free  from  carbon  dioxide;  this 
requirement  is  easily  satisfied  if  the  ventilation  is  good  and  there 
are  no  gas  burners  burning  in  a  confined  space.  In  case  the 
ventilation  is  not  good,  it  is  better  to  use  the  longer  method 
outlined  below. 

The  method  has  been  found  to  give  accurate  results  and  Cain 
claims  that  one  operator  can  make  50  determinations  in  an  8-hr, 
working  day. 

Cain  and  Maxwell1  have  also  worked  out  an  electrolytic  resis- 
tance method  which  is  still  more  rapid.  The  electric  resistance  of 
barium  hydroxide  solutions  varies  very  appreciably  with  the 
concentration. 

1  J.  I.  E.  C.,  11,  852.     The  necessary  equipment  can  be  obtained  from 
Arthur  H.  Thomas  Co.,  Philadelphia. 
2 


18 


CHEMICAL  ANALYSIS  OF  METALS 


The  absorption  apparatus  used  in  this  electrical  method  is 
essentially  a  Meyer  bulb  capable  of  holding  200  c.c.  of  solution. 
The  entrance  bulb  is  modified  so  that  a  sensitive  thermometer 
and  a  pair  of  platinized  electrodes  can  be  introduced.  By 
means  of  a  Weibel  galvanometer  and  a  specially  constructed 
bridge,  the  electric  resistance  can  be  determined  with  the  aid 
of  an  ordinary  (60  or  25-cycle)  alternating  current.  A  nomo- 
graphic  chart  has  been  worked  out  in  such  a  way  that  the  con- 
centration of  the  barium  hydroxide  solution  can  be  found  as 
soon  as  the  electric  resistance  and  temperature  are  known.  In 
carrying  out  a  series  of  analyses  at  the  Bureau  of  Standards,  the 
average  time  per  analysis  was  5  min.  Further  details  are  given 
in  Chap.  XI. 


FIG.  2. 

Cain's  original  method,  which  was  adopted  by  the  American 
Society  for  Testing  Materials  as  a  standard  in  1914,  did  not 
provide  for  the  preheating  of  the  boat,  the  furnace  was  heated 
only  to  1,000  to  1,050°  and  the  oxygen  was  introduced  at  a 
moderate  rate  for  20  to  25  min.  If  the  oxides  were  not  well  fused 
at  the  end  of  this  time,  they  were  crushed  and  reburned.  The 
barium  carbonate  was  filtered  off  under  an  atmosphere  free 
from  carbon  dioxide  as  follows: 

Connect  the  absorption  bulb  as  shown  in  Fig.  2.  S  is  a  two- 
way  stopcock  connected  with  suction.  The  bubble  tube  (Meyer 
tube)  is  fitted  with  two  rubber  stoppers  through  which  short 
pieces  of  glass  tubing  pass.  The  filter  C  contains  a  perforated 
porcplain  plate  at  the  bottom;  it  should  slip  easily  up  and  down 
the  funnel.  Cover  the  porcelain  plate  with  a  felt  of  asbestos, 


CARBON  19 

which  has  been  cleaned  by  heating  several  hours  with  strong 
hydrochloric  acid  and  then  by  washing  free  from  acid.  Place  on 
top  of  this  a  layer  of  similarly  cleansed  quartz  to  the  height 
shown  in  the  drawing.  A  mixture  of  grains  such  that  about 
one-half  passes  through  a  20-mesh  sieve  and  the  remainder 
through  a  10-mesh  sieve  is  suitable.  Instead  of  using  the  quartz 
alone,  a  mixture  of  quartz  and  asbestos  works  well.  Fill  the 
funnel  with  a  suspension  of  asbestos  and  then  wash  the  quartz  into 
the  funnel  by  means  of  a  strong  jet  of  water  from  the  wash  bottle, 
while  maintaining  gentle  suction.  In  this  way  a  filter  may  be 
prepared  which  is  efficient  and  yet  works  rapidly. 

Insert  the  stopper  in  the  funnel  and  connect  it  with  the  Meyer 
tube  as  shown  in  the  drawing  and  apply  very  gentle  suction. 
When  necessary  open  Ps  to  admit  air  back  of  the  liquid  after  the 
contents  of  the  tube  have  all  been  transferred  to  the  filter  bottle, 
half  fill  the  large  bulb  nearest  B  with  water  by  opening  the  pinch- 
cock  PI  ;  operate  the  stopcock  S  during  this  and  the  subsequent 
operations  so  as  to  maintain  gentle  suction.  Manipulate  the 
tube  M  so  as  to  bring  the  wash  water  in  contact  with  all  parts  of 
the  interior  and  then  suck  out  the  water  through  C;  during  this 
and  the  subsequent  washings  leave  the  pinchcock  P%  open. 
After  eight  washings,  allowing  the  wash  water  to  drain  off  thor- 
oughly each  time,  detach  M  and  complete  the  washing  by  filling 
C  to  the  top  with  water  free  from  carbonic  acid,  sucking  dry  and 
repeating  the  operation  once  more.  Now  admit  air  through  the 
side  opening  of  S,  take  away  C,  and  transfer  the  contents  of  the 
filter  funnel  to  an  Erlenmeyer  flask  for  the  titration. 

Add  an  excess  of  the  standard  acid  from  a  burette  and  titrate 
the  excess  of  alkali  in  the  cold  with  standard  sodium  hydroxide, 
using  methyl  orange  as  an  indicator. 

2.  DIRECT  COMBUSTION  OF  CARBON  IN  OXYGEN— RAPID 

METHOD 

If  a  sample  of  steel  is  placed  in  a  hot  furnace  it  is  possible  to 
complete  the  combustion  and  convert  all  of  the  carbon  to  carbon 
dioxide  in  less  than  2  min.  provided  an  adequate  supply  of  oxygen 
is  furnished.  For  the  combustion  of  1  g.  of  steel  approximately 
300  c.c.  of  oxygen  are  required,  measured  at  the  laboratory  tem- 
perature. It  is  possible  to  regulate  the  supply  of  oxygen  so  that 


20 


CHEMICAL  ANALYSIS  OF  METALS 


the  rate  at  which  the  gas  issues  from  the  front  end  of  the  furnace 
is  not  rapid  at  any  time  but  it  is  advisable  to  use  an  absorption 
tube  which  is  efficient  even  when  a  rapid  current  of  gas  is  passed 
through  it.  The  absorption  bulbs  shown  in  Figs.  3,  4,  and  5 
have  proved  efficient.1 


FIG.  3. 


FIG.  4. 


FIG.  5. 


1  The  illustrations  are  reproduced  by  permission  from  the  catalog  of 
the  Arthur  H.  Thomas  Co.  They  also  furnish  directions  for  filling  the 
bulbs.  The  name  ascarite  has  been  given  to  asbestos  impregnated  with 
sodium  hydroxide  according  to  the  formula  of  Stetser  and  Norton.  The 
original  Midvale  tube  was  designed  by  H.  L.  Fevert  of  the  Midvale  Steel 
Company.  To  fill  either  of  the  Midvale  bulbs,  put  in  about  j^-in.  layer  of 
glass  wool  to  prevent  stoppage  of  outlet  tube,  then  add  ascarite  until  bulb 
is  almost  full.  It  is  suggested  that  the  absorbent  be  tamped  down  lightly 
with  a  straight  piece  of  wire.  According  to  the  designers,  the  bulb  is  used 
with  the  outlet  end  of  the  Vanier  combustion  train,  i.e.,  with  the  Vanier 
zinc  tube  and  Vanier  sulfuric  acid  bulb.  A  dryer  is  unnecessary,  as  the 
absorbent  has  the  same  drying  power  as  fresh  c.  p.  sulfuric  acid.  One 
bulb  should  absorb  about  10  g.  of  CO2.  The  outlet  end  of  the  combustion 
tube  should  be  filled  for  about  3  in.  with  asbestos  previously  ignited,  other- 
wise the  sample  will  run  high.  The  first  three  or  four  samples  are  apt  to 
run  low.  To  fill  the  Fleming  bulb,  pack  the  small  diameter  portion  of  the 
upper  chamber  and  the  upper  stopper  with  asbestos  and  the  remaining 
space  with  phosphoric  anhydride;  fill  the  lower  chamber  with  soda-lime 
containing  2  per  cent  moisture  in  20,  40  and  60-mesh  size  in  alternate 
layers  of  about  ^  in.  The  lower  stopper  and  the  lower  portion  of  the  soda- 
lime  chamber  are  packed  loosely  with  asbestos.  The  tubes  should  be  used 
in  pairs  so  that  one  serves  as  a  tare  in  weighing  the  other.  A  pair  of  tubes 
insures  the  operator  of  at  least  140  combustions.  Ascarite  can  be  used  in 
this  bulb  in  place  of  the  soda-lime. 


CARBON 


21 


The  combustion  train  as  used  by  Stetser  and  Norton  is  shown 
in  Fig.  6.  A  and  B  are  8-liter  aspirator  bottles.  B  is  filled 
with  oxygen  through  the  reducing  valve  N;  the  upper  bottle  is 
graduated  for  each  250  c.c.  The  pressure  of  the  water  in  A 
forces  the  gas  into  the  furnace  and  the  volume  of  oxygen  used 
is  measured  by  the  fall  of  the  water  in  A.  C  is  a  glass  stop- 


IV  11 


FIG.  6. 


cock  to  be  closed  when  filling  B  with  oxygen.  D  is  an  empty 
safety  bottle.  Bottle  E  is  one-third  full  of  concentrated  sulfuric 
acid  and  F  contains  ascarite  (sodium  hydroxide  and  asbestos). 
J  contains  80-mesh  zinc  and  K  contains  a  little  concentrated 
sulfuric  acid. 

Procedure. — First,  test  the  apparatus  to  see  that  it  does  not 
leak;  with  C  open  and  the  stopcock  on  K  closed,  the  pressure 
from  A  should  not  cause  gas  to  bubble  through  E  and  K  after  a 


22  CHEMICAL  ANALYSIS  OF  METALS 

few  minutes.  Then  close  C  and  slowly  open  the  stopcock  on  K. 
Fill  B  with  water,  open  the  gas  regulator  valve,  at  N,  and  force  the 
water  from  B  into  A.  When  bottle  A  is  filled,  close  the  regulator 
and  the  train  is  ready  for  the  combustion.  The  exit  end  of  the 
combustion  tube,  should  be  packed  with  some  asbestos  which  has 
been  heated  to  1,000°  in  a  current  of  oxygen  prior  to  using. 

Weigh  out  1.36  g.  of  steel1  into  the  alundum  boat  and  introduce 
it  into  the  hot  furnace  as  in  Method  1.  Open  the  stop  cock  C 
and  allow  oxygen  to  pass  through  the  apparatus;  the  sample 
should  begin  to  burn  in  about  20  sec.  If  the  sample  is  coarse  or 
the  temperature  below  1,000°C.,  the  combustion  may  be  delayed. 
About  500  c.c.  of  gas  should  be  allowed  for  the  combustion  of  the 
steel  and  an  equal  volume  to  sweep  out  the  carbon  dioxide  into 
the  absorbing  bulb.  When,  therefore,  about  1  liter  of  oxygen 
has  passed  through  the  apparatus,  the  bulb  is  ready  to  be  weighed. 
The  time  at  which  the  sample  begins  to  burn  is  indicated  by  the 
increased  rate  of  flow  through  the  liquid  in  E',  a  similar  decrease 
marks  the  end  of  the  combustion. 

Standardization  of  the  Stetser  and  Norton  Absorption  Bulb. — 
A  freshly  filled  bulb  should  be  run  on  the  train  for  an  hour  and 
then  weighed.  It  is  not  necessary  to  run  the  gas  at  a  rapid  rate 
during  this  time.  The  bulb  is  again  attached  and  2  more 
liters  of  gas  are  run  through  at  the  usual  rate.  The  bulb  should 
show  neither  gain  nor  loss.  Should  it  do  so,  gas  must  be  run 
through  for  another  period  of  an  hour.  The  bulb  is  then  checked 
with  2  liters  of  gas.  It  should  not,  however,  be  necessary  to 
run  the  bulb  a  second  time. 

When  the  bulb  has  reached  a  constant  weight,  the  train  may 

1  The  directions  are  based  on  the  paper  of  STETSER  and  NORTON,  Iron  Age, 
102,  No.  8.  They  have  reported  the  results  of  a  carbon  determination 
within  6  min.  of  the  time  the  sample  entered  the  laboratory.  This  includes 
the  times  spent  in  drilling  the  sample  and  in  making  the  weighings.  Since 
carbon  dioxide  contains  27.27  per  cent  of  carbon  and  the  per  cent  of  carbon 
in  a  sample  of  steel  weighing  s  g.,  and  yielding  p  g.  of  carbon  dioxide  is 

— : it  is  clear  that  when  1.363  g.  of  steel  is  taken  for  analysis,  — ~r^™ 

S  l.oOo 

=  20  p.  In  other  words,  multiplying  the  weight  of  carbon  dioxide  by  2 
and  moving  the  decimal  point  1  place  to  the  right  gives  the  per  cent  of 
carbon.  In  this  case,  the  steel  should  be  only  weighed  to  the  nearest  centi- 
gram and  the  absorption  bulb  to  the  nearest  half  milligram. 


CARBON 


23 


be  checked  by  running  a  government  standard.1  A  fresh  bulb 
in  ay  show  slightly  low  results  on  the  first  three  analyses.  When 
filled  with  ascarite,  one  bulb  will  absorb  from  10  to  15  g.  of  carbon 
dioxide  without  refilling. 

3.    DETERMINATION    OF    CARBON    BY  THE   CORLEIS  METHOD2 

Principle. — Iron  and  steel  samples  of  suitable  fineness  are  dis- 
solved by  boiling  with  a  mixture  of  chromic  and  sulfuric 
acids,  which  causes  the  oxidation  of  nearly  all  the  carbon 
to  carbon  dioxide.  A  little  of  the  carbon  is  usually  set  free  as 
carbon  monoxide  or  as  hydrocarbon  unless  cer- 
tain precautions  are  taken.  Corleis  found  that 
the  formation  of  such  carbon  compounds  is 
greatly  reduced  by  the  addition  of  copper  sulfate 
solution,  but  it  is  always  best  to  heat  the  gases 
mixed  with  air  in  order  to  be  certain  that  all  the 
carbon  is  in  the  form  of  carbon  dioxide.  The 
carbon  dioxide  formed  is  absorbed  by  soda-lime 
contained  in  a  U-tube  or  by  caustic  potash  solu- 
tion in  a  Geissler  bulb.  From  the  gain  in  weight, 
the  amount  of  carbon  in  the  sample  is  calculated. 

Apparatus  and  Necessary  Solutions. — For  com- 
bustion with  chrome-sulfuric  acid,  the  Corleis 
flask  K  with  condenser  is  used  (Fig.  7).  There 
is  a  ground-glass  connection  between  the  con- 
denser and  the  flask. 

To  keep  the  flask  from  breaking  when  it  is 
heated,  either  support  it  on  wire  gauze  or  cover 
the  bottom  with  asbestos  paper  as  shown  in 
Fig.  8.  In  the  latter  case,  cut  out  suitably 
shaped  pieces  of  asbestos  paper  (about  0.5  mm. 
thick),  wet  them  with  water,  stick  them  to  the 
bottom  of  the  flask,  and  allow  them  to  dry  a 
little  while  in  a  drying  closet  at  110°. 

The  arrangement  of  the  entire  apparatus  is  shown  in  Fig.  8. 
Air  is  passed  through  the  apparatus  either  by  applying  suction 

1  Carefully  analyzed  samples  of  various  kinds  of  steel  can  be  obtained 
from  the  Bureau  of  Standards  at  Washington,  D.  C. 

2  Stahl  u.  Eisen,  14,  381  (1894). 


FIG.  7. 


24 


CHEMICAL  ANALYSIS  OF  METALS 


at  W  or  from  a  gasometer  leading  to  W\.  To  purify  the  air, 
place  concentrated  caustic  potash  solution  (1:1)  in  the  wash 
bottles  Wi  and  W2  and  soda-lime  in  the  U-tube,  U.  Instead  of 
these  three  tubes,  a  single  soda-lime  tower,  with  concentrated 
caustic  potash  solution  at  the  bottom  may  be  used.1 

The  gases  from  the  combustion  flask  pass  first  through  a  small 
wash  bottle,  S,  containing  concentrated  sulfuric  acid.  The  glass 
tubing  through  which  the  gas  enters  should  not  dip  into  the  sul- 
furic acid,  but  should  end  a  few  millimeters  above  the  surface  of 
the  liquid.  This  flask  has  the  function  of  holding  back  water 
vapor  and  sulfuric  acid  fumes  from  the  boiling  solution,  with- 
out any  danger  of  retaining  appreciable  quantities  of  the  hydro- 
carbons in  the  sulfuric  acid. 


FIG 


To  S,  attach  a  small  combustion  tube,  V,  made  of  difficultly 
fusible  glass  or  of  porcelain  and  containing  copper  oxide  or 
platinized  asbestos.2 

If  a  glass  tube  is  used,  wrap  it  in  iron  gauze  to  prevent  it  from 
breaking  when  heated.  The  purpose  of  this  combustion  tube  is 
to  convert  traces  of  carbon  monoxide,  or  of  hydrocarbons,  into 
carbon  dioxide. 

The  use  of  copper  sulfate  in  the  oxidizing  liquid,  however, 

lcf.  TREADWELL-HALL,  "Text-book  of  Analytical  Chemistry,"  Vol.  11. 

2  The  platinum  capillary  combustion  tubes  so  frequently  recommended 
have  not  given  satisfaction;  on  continued  use  the  platinum  crystallizes 
and  becomes  permeable  to  gases. 


CARBON  25 

prevents  the  loss  of  more  than  2  per  cent  of  the  total  amount  of 
carbon  present  in  any  sample  of  ordinary  iron  or  steel.  In 
commercial  work,  therefore,  this  combustion  tube  may  be  omitted. 
Moreover,  results  obtained  in  test  analyses  with  pure  sodium 
oxalate  show  that  the  tendency  of  the  method  is  to  give  results 
that  are  slightly  high,  which  is  another  reason  why  this  com- 
bustion tube  may  be  omitted.  In  that  case,  connect  the  flask  K 
directly  with  a  small  tube  containing  solid  chromic-acid  anhy- 
dride, between  plugs  of  glass  wool,  and  from  this  lead  the  gas 
into  a  U-tube  containing  a  few  glass  beads  wet  with  concentrated 
sulfuric  acid.  Place  a  little  glass  wool  in  each  arm  of  this 
U-tube  to  break  up  any  bubbles  of  sulfuric  acid  that  may  form 
during  the  analysis.  Then,  with  the  omission  of  S  and  of  V,  the 
arrangement  is  the  same  as  shown  in  the  drawing. 

The  last  traces  of  moisture  must  be  removed  from  the  gases 
before  the  carbon  dioxide  is  absorbed.  This  is  accomplished  by 
means  of  the  small  U-tube,  MI,  containing  calcium  chloride  or 
phosphorus  pentoxide  between  plugs  of  cotton  wool. 

From  this  drying  tube,  the  gases  pass  into  the  weighed  soda- 
lime  tubes  N  i  and  N^  in  which  the  carbon  dioxide  is  absorbed. 
Usually  all  of  the  carbon  dioxide  is  absorbed  in  the  first 
tube.  If  the  second  tube  begins  to  gain  in  weight,  it  is  a 
sign  that  the  first  tube  is  nearly  exhausted.  When  this  hap- 
pens, refill  the  first  tube  and  then  use  it  as  the  second  tube  in 
the  train. 

When  carbon  dioxide  reacts  with  soda-lime,  water  is  set  free. 
To  prevent  the  loss  of  this  moisture,  each  tube  must  contain  a 
little  calcium  chloride  or  phosphorus  pentoxide.  Fill  the  arm 
through  which  the  gas  enters  with  small  pieces  of  soda-lime  and 
fill  half  of  the  other  arm  with  soda-lime.  Then  cover  the  soda- 
lime  with  a  small  piece  of  glass  wool  and  fill  up  the  tube  with  dry 
calcium  chloride  (or  phosphorus  pentoxide).  In  the  top  of  each 
arm  of  the  U-tube,  place  a  plug  of  cotton  wool.  The  kernels  of 
soda-lime  and  of  drying  agent  should  be  from  1  to  1.5  mm.  in 
diameter;  if  much  powder  is  present,  it  must  be  sifted  out  to 
avoid  stopping  up  the  tube.  Too  large  lumps  of  either  soda- 
lime  or  drying  agent  must  not  be  used  and  the  tubes  must  be 
filled  tightly,  or  some  gas  may  escape  that  should  be  absorbed. 

As  an  added  precaution,  the  second  soda-lime  tube  is  connected 


26  CHEMICAL  ANALYSIS  OF  METALS 

with  a  calcium  chloride  (or  phosphorus  pentoxide  tube)  W2  and 
this  in  turn  is  connected  with  a  safety  wash  bottle,  W,  containing 
concentrated  caustic  potash  solution;  there  is  then  no  chance  of 
water  vapor  or  carbon  dioxide  being  drawn  back  into  the  weighed 
tubes  from  the  atmosphere.  The  wash  bottle,  TF,  also  serves 
to  indicate  the  rate  at  which  the  gas  is  passing  through  the 
apparatus. 

Connections  between  the  different  parts  of  the  apparatus  are 
made  by  rubber  tubing.  In  setting  up  the  apparatus,  take  care 
that  all  the  connections  to  the  right  of  the  Corleis  flask  are 
tight  (glass  on  glass) ;  in  no  case  should  the  ends  of  the  glass  tub- 
ing be  separated  by  empty  sections  of  rubber  tubing. 

The  following  solutions  are  necessary: 

(a)  Chromic  Acid  Solution. — Dissolve  720  g.  of  chromic  acid 
anhydride,  which  need  not  be  chemically  pure  but  should  be 
practically  free  from  organic  matter,  in  700  c.c.  of  water. 

(b)  Copper  Sulfate  Solution. — Dissolve  400  g.  of  copper  sul- 
fate  crystals  in  water  and  dilute  the  solution  to  2  liters. 

Preliminary  Boiling  of  the  Chrome-sulfuric  Acid  Solution. — 
Remove  the  condenser  from  the  flask  K,  and  introduce  35  c.c. 
of  the  chromic-acid  solution  (a),  150  c.c.  of  the  copper  sulfate 
solution  (b)  and  200  c.c.  of  concentrated  sulfuric  acid  (d.  1.84). 

Replace  the  condenser  and  start  a  stream  of  water  running 
through  it.  Boil  the  mixture  in  the  flask  to  remove  any  organic 
matter  which  may  be  present,  with  the  soda-lime  tubes  discon- 
nected from  the  flask.  While  the  solution  is  boiling,  pass  a  slow 
stream  of  purified  air  through  the  apparatus  and  heat  the  small 
combustion  tube  V.  Boil  the  solution  for  at  least  an  hour  in 
order  to  be  sure  that  in  subsequent  work  no  carbon  dioxide,  or 
other  gases  absorbed  by  soda-lime,  will  be  generated  from  carbon 
in  the  reagents.  Then  remove  the  flame  and  allow  the  apparatus 
to  cool  in  a  current  of  air. 

Before  starting  an  analysis  it  is  advisable  to  run  a  blank  on  the 
apparatus,  to  find  out  how  much  the  soda-lime  tubes  change  in 
weight  without  the  introduction  of  any  substance  to  be  analyzed. 

Blank  Run. — Rub  the  soda-lime  tubes  with  a  piece  of  chamois 
or  a  clean  linen  cloth,  allow  them  to  stand  in  the  balance  case  for 
at  least  half  an  hour,  then  open  the  stopcocks  for  an  instant  to 
equalize  the  pressure  and  weigh  them  accurately  to  0.0002  g. 


CARBON  27 

Connect  the  weighed  tubes  to  the  rest  of  the  train,  open  the 
stopcocks  and  pass  a  slow  stream  of  air  free  from  carbon  dioxide 
through  the  apparatus.  Boil  the  contents  of  the  Corleis  flask 
and  heat  the  combustion  tube  for  2  or  3  hr.  (the  usual  length 
of  time  for  a  combustion).  Then  remove  the  soda-lime  tubes, 
close  the  stopcocks  and  place  the  tubes  in  the  balance  case. 
Remove  the  flame  from  beneath  the  Corleis  flask  and  weigh  the 
tubes,  under  the  same  conditions  as  before,  after  they  have 
remained  at  least  J/9  nr'  in  the  balance  case. 

If  much  more  than  0.001  g.  gain  in  weight  is  found  in  the  blank 
determination,  something  is  wrong.  Besides  possible  impurities 
in  the  chromic  acid,  it  may  be  that  small  particles  of  soda-lime  or 
of  drying  agent  have  lodged  in  the  glass  tubing  beyond  the  stop- 
cocks, either  due  to  a  too  rapid  passage  of  the  air  current  or  to 
faulty  filling  of  the  tubes.  In  such  a  case  the  tubes  would  gain  in 
weight  constantly  if  left  in  the  air,  owing  to  absorption  of  carbon 
dioxide  or  of  water.  Care  should  be  taken,  therefore,  to  see  that 
the  tubing  is  free  from  soda-lime  or  drying  agent.  If  necessary, 
the  inside  of  the  tubes  may  be  wiped  clean  with  small  rolls  of  filter 
paper. 

Slight  gains  in  weight  in  the  absorption  tubes,  which  are  almost 
always  observed  in  the  blank,  should  be  allowed  for  in  the 
determination. 

Procedure. — While  the  acid  solution  in  the  flask  is  cooling, 
weigh  the  soda-lime  tubes  as  previously  described  and  also  the 
sample  of  iron  or  steel,  the  carbon  content  of  which  is  to  be 
determined. 

The  weight  of  sample  taken  for  analysis  should  be  determined 
by  its  probable  carbon  content.  Of  cast  iron,  with  3  per  cent  or 
more  of  carbon,  take  1  g. ;  of  steel  with  0.3  per  cent  or  more  take 
3  g.;  and  of  mild  steel  or  wrought  iron  take  5  g.1  Weigh  the 

1  In  weighing  out  samples  it  is  a  waste  of  time  to  weigh  accurately  to 
decimal  places  beyond  those  which  affect  the  analysis.  In  the  determina- 
tion of  carbon  in  steel,  the  absolute  accuracy  is  determined  largely  by  the 
degree  of  accuracy  to  which  the  soda-lime  tubes,  used  for  absorbing  the 
carbon  dioxide,  can  be  weighed.  Unless  particular  precautions  are  taken, 
such  as  reducing  the  weighings  to  vacuum,  etc.,  the  difference  between  the 
weights  of  the  soda-lime  tubes  before  and  after  the  analysis  cannot  be  as- 
sumed to  be  nearer  than  0.001  g.  to  the  truth.  As  a  general  rule,  the  next  to 
the  last  significant  figure  in  any  value  should  not  vary  by  more  than  one  or 


28  CHEMICAL  ANALYSIS  OF  METALS 

sample  into  a  porcelain  crucible,  a  glass-stoppered  weighing  tube, 
or,  if  it  can  be  obtained  in  powder  form  (e.g.,  gray  cast  iron),  into 
a  small  glass  basket  which  can  be  suspended,  by  means  of  fine 
platinum  wire,  from  the  hook  which  is  usually  provided  on  the 
end  of  the  condenser,  so  that  the  sample  is  immersed  in  the 
liquid  in  the  flask.1  After  the  chrome-sulfuric  acid  solution  has 
cooled  sufficiently,  connect  the  soda-lime  tubes  with  the  appara- 
tus and  pour  a  little  sulf uric  acid  into  the  funnel  at  the  top  of  the 
condenser  to  act  as  a  seal;  then  test  the  entire  apparatus  to  see 
if  it  is  tight.  To  do  this,  close  all  the  stopcocks  in  the  absorp- 
tion train  and  open  the  cock  at  the  air  supply  to  the  Corleis  flask. 
After  a  short  time  no  more  bubbles  should  pass  through  the  Cor- 
leis flask.  If  bubbles  do  form,  a  leak  is  indicated  between  the 
Corleis  flask  and  the  calcium  chloride  tube  u\.  When  this  sec- 
tion is  found  to  be  tight,  open  the  first  stopcock  in  the  calcium 
chloride  (or  phosphorus  pentoxide)  tube;  if  after  waiting  a  short 
time  the  current  of  air  through  the  Corleis  flask  again  stops,  open 

two  units.  According  to  this  rule,  therefore,  the  soda-lime  tubes  should  be 
weighed  as  carefully  as  possible  to  four  decimal  places,  which  is  possible  with 
the  usual  analytical  balance.  In  the  case  of  a  sample  of  steel  with  1  per 
cent  carbon,  a  3-g.  sample  will  yield  0.110  g.  of  carbon  dioxide  and  an 
error  of  0.001  g.  in  this  weight  will  correspond  to  0.01  per  cent  carbon,  or 
to  one-hundredth  of  the  entire  carbon  content.  This  precision  is  satis- 
factory here.  An  error  of  0.03  g.  in  the  original  weight  would  correspond 
to  the  same  fractional  error.  If,  therefore,  the  original  sample  is  weighed 
to  the  nearest  centigram,  any  error  introduced  by  neglecting  the  following 
decimal  places  will  not  have  an  appreciable  effect  upon  the  final  result  and 
any  balance  accurate  to  0.01  g.  can  be  used  for  weighing  out  the  sample. 
It  is  not  only  a  waste  of  time,  but  unscientific  in  principle,  to  determine 
values  smaller  than  those  which  have  a  noticeable  effect  upon  the  result. 

In  weighing  out  smaller  samples  it  is  usually  necessary  to  weigh  more  ac- 
curately but  with  cast  iron  the  sample  is  rarely  perfectly  homogeneous  so 
that  in  carbon  determinations  even  with  a  1-g.  sample,  it  is  sufficient  if 
the  original  weighing  is  accurate  to  0.01  g. 

1  For  obtaining  representative  samples  and  for  the  method  of  weighing 
small  samples  for  analysis  the  precautions  mentioned  in  Part  II  of  the 
book  should  be  taken. 

The  shavings  for  the  combustion  with  chrome-sulfuric  acid  treatment 
should  not  be  more  than  1  mm.  thick  if  the  combustion  is  to  be  finished  in 
2  or  3  hr.  Thicker  pieces  should  be  hammered,  broken  or  rolled  before 
cutting.  Hard-drawn  wire  or  high-silicon  tungsten  steel  often  requires  3  or 
4  hr.  for  combustion  even  if  it  is  finely  divided. 


CARBON  29 

tho  next  stopcock  and  so  on  up  to  the  last  stopcock  on  the  final 
calcium  chloride  tube  w2.  After  the  apparatus  has  been  shown 
to  be  tight1  and  the  air  supply  has  been  shut  off,  slowly  open  the 
last  stopcock  so  that  the  excess  of  air  will  escape  from  the  appara- 
tus without  rushing.  A  sudden  rush  of  air  might  carry  calcium 
chloride  (or  phosphorus  pentoxide)  dust  either  into  or  out  of  the 
weighed  tubes,  in  each  case  causing  a  change  in  weight. 

When  the  excess  of  air  has  escaped,  remove  the  condenser  and 
pour  the  weighed  sample  into  the  flask,  or,  if  the  sample  has  been 
weighed  into  a  small  glass  basket,  hang  this  on  the  hook.  Re- 
place the  condenser  at  once  and  pour  a  little  strong  sulfuric  acid 
over  the  connection  between  the  condenser  and  the  flask  to  make 
a  tight  joint.  Raise  the  condenser  again,  just  a  trifle,  so  that  a 
little  of  the  sulfuric  acid  can  run  into  the  flask  to  wash  down  any 
particles  of  the  sample  which  may  have  stuck  to  the  glass. 

Now  light  the  gas  under  the  combustion  tube  V  and  cause  a 
slow  stream  of  air,  free  from  carbon  dioxide,  to  pass  slowly 
through  the  apparatus.  Heat  the  Corleis  flask,  slowly  at  first, 
until  the  acid  boils.2 

Continue  the  boiling  for  about  3  hr.,  which  is  usually  long 
enough  to  insure  the  complete  solution  and  oxidation  of  the 
sample,  unless  it  was  in  too  coarse  a  condition.  During  this  time 
the  apparatus  should  be  watched  to  see  that  the  acid  does  not 
boil  too  violently,  and  that  the  air  is  run  at  the  proper  rate,  not 
more  than  three  bubbles  a  second.  At  the  start  if  the  contents  of 
the  flask  are  heated  too  quickly,  particularly  just  before  the 
solution  boils,  there  is  some  danger  of  liquid  sucking  back  toward 
the  purification  train.  This  is  prevented  by  lowering  the  flame 
and  increasing  the  speed  of  the  air  current.  If,  by  accident, 
some  of  the  liquid  gets  back  into  the  tube  U,  the  determination  is 

1  If,  instead  of  using  an  air  reservoir  in  the  experiment,  suction  is  applied 
at  the  other  end  of  the  train,  the  manner  of  testing  for  leaks  is  the  reverse. 
Gentle  suction  should  be  used  in  making  the  test  and  care  should  be  taken 
not  to  let  the  air  in  too  rapidly  after  the  test. 

2  The  current  of  air  must  be  started  as  soon  as  the  sample  has  been  intro- 
duced.    As  the  cold  chromic-acid  mixture  has  slight  oxidizing  power  it  is 
possible  for  small  amounts  of  hydrogen  and  hydrocarbons  to  form.     If 
these  gases  are  not  diluted  and  removed  by  the  air  current,  they  form  mix- 
tures with  the  air  in  the  apparatus  which,  at  certain  concentrations  of 
hydrogen  and  hydrocarbon,  may  explode  in  the  combustion  tube. 


30  CHEMICAL  ANALYSIS  OF  METALS 

spoiled.  During  the  last  15  min.  of  the  boiling,  it  is  well  to 
increase  the  rate  at  which  the  air  is  passing  so  that  it  will  drive 
over  the  last  traces  of  carbon  dioxide  into  the  absorption  train. 

When  the  combustion  is  complete,  stop  the  current  of  air  and 
turn  out  the  gas  flames.  Close  the  stopcocks  of  all  the  U-tubes 
that  are  in  front  of  the  flask  and  remove  the  soda-lime  tubes. 
Allow  these  tubes  to  stand  in  the  balance  case  for  at  least  ^  nr- 
arid  weigh  them  witli  the  usual  precautions. 

When  the  contents  of  the  Corleis  flask  have  cooled,  remove  the 
condenser  and  observe  carefully  whether  there  is  any  undissolved 
sample  in  the  bottom  of  the  flask.  In  case  of  doubt,  this  can  be 
seen  easily  by  pouring  the  contents  of  the  flask  into  a  large  beaker 
containing  considerable  water.  In  most  cases  this  is  unnecessary 
and  the  solution  may  be  used  again  for  another  determination. 
The  quantities  of  reagents  used  are  sufficient  for  the  combustion 
of  at  least  10  g.  of  steel. 

If  some  undissolved  material  should  be  noticed  in  the  bottom 
of  the  flask,  it  is  necessary  on  repeating  the  experiment  to  use 
finer  material  or  to  continue  the  boiling  for  a  longer  period.  In 
no  case,  however,  is  it  permissible  to  sift  a  sample  of  cast  iron 
because  the  fine  powder  is  likely  to  contain  more  graphite  than 
the  larger  particles.  Some  kinds  of  iron  alloys  will  not  dissolve 
in  the  acid ;  the  carbon  in  such  alloys  should  not  be  determined  by 
this  method. 

Computation. — If  p  represents  the  gain  in  weight  of  the  soda- 
lime  tube  (or  tubes)  in  the  analysis  of  a  sample  weighing  s  g.,  then 

27.3  X  p 


Per  cent  C  = 


8 


ACCURACY  OF  THE  VALUES  FOUND  BY  THE  CHROME-SULFURIC 

ACID  METHOD 

Allowing  for  differences  in  the  composition  of  the  samples,  as 
discussed  in  Part  II  of  this  book,  the  errors  which  may  occur  in 
the  chrome-sulfuric  acid  method  are  traceable  chiefly  to  errors  in 
weighing  and  to  the  gain  in  weight  of  the  soda-lime  tube  from 
some  source  other  than  the  carbon  in  the  sample. 

Assuming  that  the  errors  of  weighing  are  not  greater  than 
±0.001  g.  and  that  the  first  soda-lime  tube  has  an  average  weight 


CARBON  31 

of  0.002  g.  too  high  the  total  error  in  a  properly  conducted  analysis 
probably  lies  between  +0.001  to  +0.003  g.  carbon  dioxide. 

The  error  in  all  cases  would  be  found  in  the  secoad  decimal 
place  of  the  calculated  percentage  and  would  be,  for  example,  be- 
tween 0.01  and  0.03  per  cent  with  a  3-g.  sample  or  between  0.005 
and  0.02  per  cent  with  a  5-g.  sample. 

It  follows  from  this  that  the  carbon  content  is  uncertain  in  the 
second  decimal  and  it  is  sometimes  customary,  for  this  reason, 
to  write  the  second  figure  small. 

The  use  of  a  third  decimal,  except  in  such  cases  where  very  un- 
usual precautions  have  been  taken,  is  not  only  unnecessary  but 
also  shows  that  the  analyst  is  ignorant  of  the  probable  error  of 
the  method. 

If  the  carbon  determination  is  carefully  carried  out,  the  follow- 
ing values  may  be  taken  as  permissible  variations  in  the  analysis 
of  samples  weighing  about  3  g. 


With  a  carbon  content  Greatest  allowable  deviation 
_rom                to 
0.02          0.15  per  cent  ±  0.005  per  cent 

0 . 15          1 . 00  per  cent  ±  0 . 010  per  cent 

1 . 00          2 . 00  per  cent  ±  0 . 020  per  cent 

2 . 00  and  higher  per  cent  ±  0 . 030  per  cent 

Greater  accuracy,  as  for  example,  that  given  by  Bischoff1  for 
low  carbon  material,  can  scarcely  be  attained. 

APPLICABILITY  OF  THE   CHROME-SULFURIC   ACID  PROCESS 

The  chrome-sulfuric  acid  method  is  suitable  for  all  sorts  of 
irons,  steels  and  special  steels  as  well  as  for  numerous  other  metals 
and  alloys  used  in  the  steel  industry.  The  following  substances 
can  be  decomposed  without  leaving  a  residue;  ferro-manganese, 
chrome-manganese,  ferro-vanadium,  ferro-molybdenum,  ferro- 
titanium,  manganese-titanium,  ferro-boron,  metallic  nickel  and 
metallic  molybdenum  in  the  form  of  fine  powder.  The  method 
cannot  be  used  for  the  following  materials  which  are  scarcely 
attacked  after  4  hr.  treatment;  ferro- silicon,  ferro- tungsten, 
metallic  tungsten,  ferro-phosphorus,  ferro-chromium,  and  metallic 
molybdenum  either  as  wire  or  as  sheet. 

1  Stahl  u.  Eisen,  22,  727. 


32  CHEMICAL  ANALYSIS  OF  METALS 

4.  DETERMINATION   OF  TOTAL   CARBON  BY  THE  POTASSIUM- 
CUPRIC-CHLORIDE  METHOD 

This  method,  for  a  long  time  considered  better  than  a  direct 
combustion,  does  not  give  reliable  results  with  certain  alloy 
steels,  especially  chrome-tungsten  steel,  probably  on  account  of 
some  carbon  being  lost  as  hydrocarbon.  It  will  give  reliable 
results  with  all  ordinary  samples  of  iron  and  steel. 

After  the  removal  of  the  iron,  the  carbon  can  be  determined 
by  combustion  either  in  an  electric  or  gas-heated  furnace. 
Inasmuch  as  many  laboratories  are  not  equipped  with  electric 
furnaces,  especially  those  laboratories  which  use  the  double 
chloride  method,  the  procedure  will  be  described  as  carried  out 
with  a  gas-heated  furnace. 

Principle. — When  metallic  iron  is  placed  in  contact  with  a 
solution  of  a  cupric  salt,  the  iron,  because  of  its  greater  solu- 
tion tension  replaces  the  copper  which  is  precipitated  upon  the 
remaining  iron.  In  the  presence  of  an  excess  of  cupric  salt,  the 
deposited  copper  reacts  to  form  cuprous  chloride  which  is  kept 
in  solution  by  the  potassium  chloride,  and  to  some  extent  by 
the  hydrochloric  acid,  with  which  it  forms  a  soluble  double  salt. 
The  reactions  may  be  expressed  as  follows: 

Fe  +  CuCl2     =  FeCl2  +  Cu 
Cu  +  2CuCl2  =  Cu2Cl2 
or 

Fe  +  Cu++  =  Fe++  +  Cu 
Cu  +  Cu++  =  2Cu+ 

Since  hydrochloric  acid  reacts  with  iron  carbide  and  with  its 
solid  solution  in  iron,  setting  free  gaseous  hydrocarbons,  it  was 
at  first  thought  necessary  to  carry  out  the  treatment  with  potas- 
sium cupric  chloride  in  a  perfectly  neutral  solution  but  it  was 
found  later  that  no  hydrocarbons  were  set  free  by  dilute  hydro- 
chloric acid  in  the  presence  of  a  cupric  salt  and  that,  in  fact,  the 
presence  of  nearly  10  per  cent  by  volume  of  strong  hydrochloric 
acid  is  not  only  permissible  but  beneficial;  in  many  cases  the 
results  are  higher  and  nearer  the  truth. 

Necessary  Apparatus  and  Solutions. — The  combustion  train, 
Fig.  9,  consists  first  of  a  short  preheating  furnace  containing 


CARBON 


33 


a  glazed  porcelain  tube  filled  with  granular  cupric  oxide  between 
loose  plugs  of  ignited  asbestos.  This  serves  to  oxidize  any  gaseous 
carbon  compounds  that  may  possibly  be  present  in  the  oxygen 
supply.  Between  this  furnace,  and  the  longer,  ten-burner  com- 
bustion furnace  in  which  the  sample  is  burned,  is  a  Geissler 
bulb,  with  the  bottom  bulbs  about  two-thirds  filled  with  strong 
caustic  potash  solution  (1  :1).  This  serves  to  remove  any  car- 
bon dioxide  from  the  oxygen,  or  air,  used  in  the  combustion. 

The  combustion  tube,  made  of  glazed  porcelain,  contains 
copper  oxide  in  the  end  near  the  absorption  train,  between  plugs 
of  ignited  asbestos,  but  space  is  left  at  the  other  end  so  that  the 
sample  can  be  introduced  into  the  hottest  part  of  the  furnace. 


Absorption   Train. 


Preheater 


Gas    Furnace. 


FIG.  9. 

The  absorption  train  consists  of  a  small  bubble  tube  about  one- 
fourth  filled  with  a  saturated  solution  of  ferrous  sulfate  (60  g. 
FeSO4.7H2O  in  100  c.c.  water),  a  similar  tube  containing  about 
10  c.c.  of  a  saturated  solution  of  silver  sulfate  in  sulfuric  acid 
(d.  1.40),  a  U-tube  containing  granular  calcium  chloride  (or 
phosphorus  pentoxide)  and  a  Geissler  bulb  containing  caustic 
potash  solution  (1:2)  with  a  prolong  filled  with  calcium  chloride. 

The  purpose  of  the  ferrous  sulfate  is  to  reduce  any  chlorine 
that  may  be  evolved  during  the  combustion  of  the  residue  ob- 
tained after  treatment  with  potassium-cupric-chloride  solution. 
The  ferrous  sulfate  changes  the  chlorine  to  hydrochloric  acid 
which  is  retained  partly  as  ferric  salt;  if  any  escapes  it  is  caught 
by  the  silver  sulfate  in  the  next  tube. 

In  filling  the  calcium  chloride  tubes,  especially  the  prolong  of 


34  CHEMICAL  ANALYSIS  OF  METALS 

the  Geissler  bulb,  take  care  to  press  down  the  granular  calcium 
chloride,  using  particles  %  in.  in  diameter.  If  the  tube  is  loosely 
filled  some  moisture  is  likely  to  escape ;  for  this  reason  a  negative 
blank  is  often  obtained  by  the  beginner. 

Instead  of  the  tubes  of  ferrous  sulfate  and  silver  sulfate,  the 
use  of  anhydrous  cupric  sulfate  followed  by  anhydrous  cuprous 
chloride  has  been  recommended,  or,  as  suggested  by  E.  S. 
Johnson,  a  column  of  20-mesh  zinc  between  glass-wool  plugs  will 
serve  to  remove  either  acid  or  chlorine. 

Instead  of  the  Geissler  tube,  U-tubes  filled  with  soda-lime  and 
calcium  chloride  may  be  used  as  in  Method  3,  p.  23. 

Potassium-cupric-chloride  Solution. — Dissolve  300  g.  of  the 
double  chloride  in  water  containing  75  c.c.  of  concentrated  hydro- 
chloric acid  (d.  1.2),  and  dilute  the  solution  to  1  liter. 

Ignited  Asbestos. — Place  the  asbestos  in  a  dish  and  heat  it 
to  bright  redness  in  a  muffle  furnace.  Remove  the  dish,  allow 
the  asbestos  to  cool  somewhat,  and  turn  over  the  asbestos. 
Again  heat  to  redness  in  the  muffle  furnace.  While  cooling, 
keep  the  dish  covered  to  prevent  dirt  from  falling  into  it.  If 
necessary,  cut  the  ignited  asbestos  into  short  pieces  and  add 
enough  water  to  form  a  fairly  thick  suspension. 

Procedure. — Weigh  out  3  g.  of  ordinary  steel,  or  1  g.  of  pig 
iron,  into  a  400-c.c.  beaker  and  cover  the  sample  with  100  c.c. 
of  the  double  chloride  solution  for  each  grain  of  metal  taken. 
Stir  the  solution  with  some  form  of  mechanical  stirrer  until  all  the 
iron  has  dissolved.  It  is  very  easy  to  tell  when  the  solution  is 
complete  by  holding  the  beaker  up  to  the  light.  If  pieces  of 
undissolved  metal  remain,  they  will  be  coated  with  metallic 
copper,  which  is  readily  distinguished  from  the  black  carbona- 
ceous residue. 

Prepare  an  asbestos  filter  by  placing  a  coil  of  fairly  heavy  cop- 
per wire  in  the  bottom  of  a  tube  funnel,  like  that  shown  in  Fig. 
2,  at  C,  and  cover  this  coil  with  about  an  inch  of  wet,  ignited  as- 
bestos. Filter  off  the  residue  from  the  double  chloride  treat- 
ment and  wash  out  the  beaker  with  10  c.c.  of  double  chloride 
solution  diluted  with  an  equal  volume  of  water.  Moderate  suc- 
tion may  be  used  but  this  is  not  necessary.  Transfer  all  of  the 
residue  to  the  filter  by  means  of  dilute  hydrochloric  acid  from 
a  wash  bottle.  Finally  wash  the  residue  on  the  filter  with  hot 


CARBON  35 

water  until  free  from  chloride.  Carefully  push  up  the  filter  from 
the  funnel  and  transfer  it,  bottom  down,  to  a  clean  watch- 
glass.  Rub  the  side  of  the  funnel  with  ignited  asbestos  to  remove 
any  adhering  carbon,  and  add  this  to  the  main  portion  on  the 
watch-glass.  Cover  and  dry  for  an  hour  or  two  at  a  temperature 
between  95  and  100°.  It  is  then  ready  for  the  combustion. 

In  starting  with  a  freshly  filled  combustion  tube,  it  should  be 
heated  %  hr.  while  passing  a  current  of  oxygen  through  it. 
Then  attach  the  absorption  tube,  weighed  with  the  same  precau- 
tions as  described  for  weighing  the  soda-lime  tubes  in  Method  3, 
p.  26,  and  make  a  blank  run  to  be  sure  the  apparatus  is  ready 
for  use.  Heat  the  tube  red  hot  and  pass  oxygen  through  it  for  20 
min.,  at  a  rate  such  that  two  or  three  bubbles  per  second  pass 
through  the  absorption  tube,  then  turn  out  the  burners  under 
the  back  end  of  the  furnace,  where  the  sample  is  to  be  intro- 
duced, and  pass  air  through  the  tube  for  another  20  min. 
This  may  be  done  either  by  having  an  air  reservoir  under 
pressure  or  by  applying  suction  at  the  front  end  of  the  furnace. 
A  simple  way  of  getting  suction  is  to  have  two  large  bottles, 
one  on  the  working  bench  and  the  other  on  the  floor.  By  filling 
the  upper  bottle  with  water  and  allowing  it  to  siphon  slowly  into 
the  lower  bottle,  sufficient  suction  is  obtained.  In  this  way  the 
volume  of  air  passed  through  the  combustion  apparatus  is 
shown. 

If  after  the  blank  run,  the  absorption  tube  does  not  show  over 
0.0010  g.  change  in  weight,  the  apparatus  is  ready  for  use. 

Push  the  dried  asbestos  well  into  the  back  end  of  the  furnace 
and  wipe  out  the  watch-glass  with  dry,  ignited  asbestos.  Make 
sure  that  the  carbon  reaches  far  enough  into  the  tube  to  get  the 
full  heat  of  the  furnace.  If  the  combustion  tube  is  cold,  light 
the  preheating  furnace  and  turn  on  the  oxygen,  allowing  it  to 
pass  through  the  absorption  bulb  at  a  maximum  rate  of  three 
bubbles  a  second.  Light  the  two  forward  burners  under  the 
combustion  tube  and  gradually  turn  up  the  flames  until  this  end 
of  the  furnace  tube  is  red  hot.  Then  light  the  next  burner  and 
continue  in  this  way  until  finally  the  whole  furnace  is  hot. 

To  avoid  burning  the  rubber  stoppers  at  the  ends  of  the  com- 
bustion tube,  place  shields  of  heavy  asbestos  board  around  each 
end  of  the  tube  where  it  projects  from  the  furnace  and  wrap 


36  CHEMICAL  ANALYSIS  OF  METALS 

each  end  near  the  stopper  with  a  narrow  band  made  of  several 
thicknesses  of  cheese  cloth  with  the  ends  dipping  in  cold  water. 
After  20  min.  have  elapsed  from  the  time  the  last  burner  was 
lighted,  stop  the  current  of  oxygen  and  pass  a  current  of  air 
through  the  tube  at  the  same  rate  to  sweep  out  all  of  the  carbon 
dioxide.  Gradually  turn  down  the  burners  under  the  tube,  but 
if  it  is  to  be  used  immediately  for  another  combustion,  it  is 
best  to  keep  the  front  end  hot.  Finally  detach  the  Geissler 
bulb  and  weigh  with  the  usual  precautions. 

NOTES. — Instead  of  oxidizing  the  residue  from  the  double  chloride 
treatment  by  a  dry  combustion,  many  chemists  prefer  to  oxidize  it  in 
the  wet  way  by  means  of  chrome-sulfuric  acid,  as  in  Method  3,  p.  23. 

Instead  of  a  combustion  tube,  the  Gooch  tubulated  crucible  or  the 
Shinier  crucible  may  be  used.  When  the  combustion  is  carried  out  in  a 
crucible,  place  after  the  crucible  a  copper  tube  about  10  in.  long  and  21 6 
in.  inside  diameter,  with  its  ends  cooled  by  water  jackets.  In  the 
center  of  this  tube  place  a  disk  of  platinum  gauze  and  a  3-in.  roll  of  silver 
foil,  on  the  side  near  the  crucible,  and  copper  oxide  on  the  other  side. 
Plug  the  ends  of  this  tube  with  glass  wool  and  heat  it  with  a  burner  which 
is  fitted  with  a  flame  spreader. 

Test  Analyses. — To  illustrate  the  accuracy  of  the  above 
method,  the  following  values  are  taken  quite  at  random  from 
certificates  issued  by  the  Bureau  of  Standards  at  Washington, 
D.  C.  At  the  present  time  most  of  the  analyses  made  at  the 
Bureau  itself  are  by  a  direct  combustion  method. 

A  sample  of  pig  iron  was  analyzed  by  the  direct  combustion 
method  by  five  different  chemists  and  the  average  value  obtained 
was  2.464  per  cent  carbon;  eight  chemists  obtained  an  average 
value  of  2.461  per  cent  carbon  by  the  solution  and  combustion 
method. 

In  a  sample  of  Bessemer  steel,  nine  chemists  obtained  the 
value  0.805  per  cent  carbon  by  direct  combustion  and  three 
chemists  obtained  an  average  value  of  0.806  per  cent  carbon  by 
solution  and  combustion. 

With  a  sample  of  vanadium  steel,  eight  chemists  obtained  an 
average  value  of  0.348  per  cent  by  direct  combustion  and  five 
chemists  obtained  an  average  value  of  0.348  per  cent  carbon  by 
solution  and  combustion. 

With  a  sample  of  nickel  steel,  seven  chemists  obtained  an 
average  value  of  0.375  per  cent  carbon  by  direct  combustion  and 


CARBON  37 

five  chemists  obtained  the  average  value  of  0.379  by  solution 
and  combustion. 

4.  DETERMINATION  OF  CARBON  BY  THE  DEISS  METHOD 

The  first  method  described  for  the  determination  of  carbon 
was  worked  out  in  the  laboratories  of  the  Bureau  of  Standards  at 
Washington,  D.  C.  The  following  method  was  recommended 
by  E.  Deiss  when  working  at  the  Royal  Testing  Bureau  near 
Berlin.  The  principle  of  the  method  is  the  same  as  the  method 
of  Cain  and  Maxwell  except  that  soda-lime  is  used  to  absorb  the 
carbon  dioxide  and  the  gain  in  weight  of  the  absorption  tube  is 
determined.  When  soda-lime  of  suitable  physical  and  chemical 
properties  is  available  it  is  thoroughly  satisfactory  as  an 
absorbent. 

Apparatus. — Principle. — On  heating  iron  and  steel  to  about 
1,100  or  1,200°  in  a  current  of  oxygen,  the  metal  is  oxidized 
completely  to  f  erroso-f  erric  oxide  and  any  other  elements  that  may 
be  present  are  also  changed  to  oxides.  Of  these  latter  elements 
carbon  and  sulfur  form  volatile  compounds  which  can  be  absorbed 
and  determined.  With  excess  of  oxygen,  carbon  forms  carbon 
dioxide  and  sulfur,  either  the  dioxide  or  the  trioxide. 

If  the  evolved  gases  were  absorbed  directly  in  a  soda-lime  tube 
and  the  carbon  content  calculated  from  the  gain  in  weight,  the 
results  might  be  too  high,  due  to  the  sulfur  present,  or  too  low  be- 
cause of  insufficient  oxidation  (formation  of  carbon  monoxide). 

In  order  to  determine  carbon  accurately,  therefore,  the  gases 
must  be  freed  from  oxides  of  sulfur  by  suitable  means  and  any 
carbon  monoxide  must  be  oxidized  to  dioxide  before  the  absorp- 
tion train  is  reached. 

Apparatus. — For  heating  the  porcelain  or  quartz  tube  in  which 
the  combustion  takes  place,  a  horizontal  tube  furnace  with  vari- 
able resistances  and  connection  with  a  high-tension  electric 
circuit  is  desirable. 

If  many  carbon  determinations  are  to  be  made  a  tube  furnace 
of  large  diameter  is  recommended ;  several  porcelain  tubes  can  be 
heated  in  it  at  the  same  time  and  with  the  use  of  only  a  little  more 
current.  A  platinum,  platinum-rhodium  thermoelement  with  a 
milli voltmeter  is  used  to  measure  the  temperature1  in  the  furnace. 

1  For  further  details  consult  LE  CHATELIER'S  "High-temperature  Measure- 
ments" (Boudouard-Burgess). 


38 


CHEMICAL  ANALYSIS  OF  METALS 


To  avoid  overloading  the  furnace  at  the  beginning  of  the  heat- 
ing it  is  best  to  have  an  ammeter  in  the  circuit. 

The  combustion  itself  takes  place  in  a  tube  made  of  quartz  or 
glazed  porcelain.  The  tube  contains  a  little  coarse  copper  oxide 
and  some  chromate  mixture.  To  prepare  the  latter,  mix  to- 
gether 9  parts  of  potassium  chromate  with  1  part  of  potassium 
dichromate,  heat  till  sintered  in  a  porcelain  crucible  and  grind  the 
sintered  mass  to  a  coarse  powder.  This  charge  would  at  once 
melt  and  lose  its  efficiency  if  placed  in  the  hottest  part  of  the  tube ; 
in  the  part  that  projects  from  the  furnace  it  is  heated  by  radiation 
sufficiently  to  effect  the  conversion  of  any  carbon  monoxide  to 
dioxide  and  of  any  sulfur  dioxide  to  sulfuric  acid  anhydride  which 
is  retained  by  the  chromate  mixture. 


Line  Voltage 


Ammeter 


Galvanometer 


FlG.    10. 


Place  a  loose  plug  of  ignited  asbestos  just  at  the  end  of  the  part 
of  the  tube  that  is  inside  the  furnace,  after  this  a  layer  of  copper 
oxide  about  2  cm.  long  and  then  an  equally  long  layer  of  chromate 
mixture,  also  between  asbestos  plugs.  The  copper  oxide  is  less 
fusible  than  the  chromate  mixture.  If,  however,  it  reaches  the  hot 
part  of  the  tube  and  melts,  the  tube  is  likely  to  crack  on  cooling. 

A  sketch  showing  the  connections  for  the  tube  furnace  and  for 
the  thermoelement  is  given  in  Fig.  10 

The  arrangement  of  the  entire  apparatus  is  shown  in  Fig.  11. 
Its  different  parts  will  be  described  in  succession  and  in  the  direc- 
tion of  the  current  of  oxygen. 


CARBON 


30 


40  CHEMICAL  ANALYSIS  OF  METALS 

The  oxygen  is  kept  in  a  gasometer  filled  from  a  tank  of  com- 
pressed gas.  In  order  to  purify  the  oxygen  from  the  gasometer 
it  is  passed  first  through  several  wash  bottles  containing  concen- 
trated caustic  potash  solution  (1:1)  then  through  a  large  soda- 
lime  tube  and  finally  through  a  tube  containing  calcium  chloride 
(or  phosphorus  pentoxide) .  A  piece  of  rubber  tubing  closed  with 
a  pinchcock  leads  from  the  last  drying-tube  to  the  combustion 
tube  or,  in  case  several  tubes  are  used  in  one  furnace,  this  rubber 
tubing  leads  to  a  forked  glass  tube  and  from  there  to  the  different 
porcelain  tubes.  The  porcelain  tubes  and  the  thermoelement  in 
its  protecting  tube  are  held  firmly  in  the  openings  of  the  furnace 
with  the  aid  of  asbestos  wool;  take  care  that  the  tubes  do  not 
come  in  direct  contact  with  one  another  or  with  the  walls  of  the 
furnace.  A  good  method  of  keeping  the  tubes  apart  is  to  use  a 
thick  piece  of  asbestos  board  with  holes  corresponding  to  the 
number  of  tubes  used  and  through  which  the  tubes  will  project 
from  both  ends  of  the  furnace. 

The  thermoelement  should  extend  far  enough  into  the  furnace 
so  that  its  junction  will  be  in  the  hottest  part  of  the  tube.  The 
wires  of  the  thermoelement  are  connected  with  the  poles  of  the 
galvanometer  and  by  closing  the  switch  in  the  main  circuit  it  is 
possible  to  tell  whether  the  connections  are  correctly  made. 
The  pointer  should  move  toward  the  scale.  Place  the  porcelain 
tubes,  filled  with  copper  oxide  and  the  chromate  mixture,  in  the 
furnace  with  the  filled  parts  at  the  front  end,  farthest  away  from 
the  oxygen  tank,  so  that  the  oxygen  passes  first  through  the 
empty  part  of  the  tube,  in  which  the  combustion  boat  is  to  be 
placed,  then  through  the  copper  oxide  and  chromate  mixture,  and 
finally  into  the  absorption  train.  The  first  tube  in  the  train 
contains  calcium  chloride  (or  phosphorus  pentoxide)  to  absorb 
moisture  from  the  gases  and  the  two  tubes  following  are  filled  with 
soda-lime  and  calcium  chloride  (or  phosphorus  pentoxide)  to 
absorb  carbon  dioxide.  These  tubes  are  filled  and  handled 
exactly  as  in  the  chrome-sulfuric  acid  method  (p.  26).  Attach 
a  safety  tube  of  concentrated  sulfuric  acid  to  the  last  soda-lime 
tube,  to  prevent  any  moisture  from  getting  back  into  the  tube  in 
case  the  gases  should  suck  back.  This  tube  also  serves  to  indicate 
the  rate  at  which  the  gases  are  passing. 

Porcelain  tubes,  glazed  on  the  outside  only,  or  quartz  tubes, 


CARBON  41 

may  be  used  for  the  combustions.  If  the  furnace  is  30  cm.  long, 
tubes  of  50-cm.  length  are  used.  A  furnace  with  an  internal 
diameter  of  50-mm.  will  hold  a  thermoelement  and  three  combus- 
tion tubes  of  12-mm.  outside  diameter. 

The  porcelain  boats  used  in  the  combustion  for  holding  the 
sample  should  preferably  be  of  unglazed  material.  To  avoid  any 
possible  fusing  of  the  boat  to  the  inner  wall  of  the  tube,  even  when 
boats  glazed  on  the  outside  are  used,  it  is  a  good  plan  to  wind 
pieces  of  asbestos  fiber  around  the  boat  about  1  cm.  from  each 
end.  When  the  boat  is  introduced  into  the  tubes  these  fibers 
prevent  it  from  coming  in  direct  contact  with  the  tube  walls. 

Procedure. — After  weighing  the  soda-lime  tubes,  using  the 
precautions  described  in  the  chrome-sulfuric  acid  method, 
weigh  the  sample  into  a  boat  which  has  been  previously  wound 
with  asbestos  fibers  and  ignited.  For  iron  and  steel  samples  with 
high-carbon  content,  a  weight  of  1  g.  is  usually  sufficient  and  this 
can  be  spread  on  a  boat  7  cm.  long,  8  mm.  wide  and  5  mm.  deep. 
For  weighing  larger  samples  (2  or  3  g.)  which  are  necessary  with 
low-carbon  material,  boats  about  13  cm.  long,  7  mm.  wide  and  6 
mm.  deep  should  be  used.  Take  care  in  filling  the  boat  not  to 
let  pieces  of  the  sample  project  over  the  edge,  as  the  molten 
oxide  formed  during  the  combustion  will  then  drop  off  and  come 
in  contact  with  the  inside  of  the  tube.  The  very  coarse  shavings 
which  sometimes  form  in  taking  the  sample  cannot  be  used  on  this 
account  and  must  be  brought  into  a  denser  and  flatter  form  by 
hammering  in  a  diamond  mortar. 

It  is  best  not  to  have  the  sample  too  fine.  Fine  shavings  and 
powder  burn  very  easily,  to  be  sure,  but  the  combustion  starts 
ao  quickly  and  proceeds  so  rapidly  that  there  is  danger  of  there 
being  an  insufficient  oxygen  supply  (formation  of  carbon  mon- 
oxide) and  there  is  also  danger  of  the  liquid  in  the  last  flask  suck- 
ing back,  unless  the  rate  of  flow  of  the  oxygen  is  increased  quickly. 
The  combustion  goes  less  violently  but  completely  with  coarse 
shavings  or  thick  pieces.  Pig  iron  chips,  2  mm.  thick,  will  burn 
readily  in  the  electric  furnace,  whereas  pieces  of  the  same  size 
will  be  attacked  scarcely  at  all  by  4  hr.  treatment  with  the 
chrome-sulfuric  acid  mixture. 

While  the  soda-lime  tubes  and  the  sample  are  being  weighed, 
pass  a  slow  current  of  oxygen  through  the  previously  ignited 


42  CHEMICAL  ANALYSIS  OF  METALS 

porcelain  (or  quartz)  tube.  Connect  the  closed  soda-lime  tubes 
in  place,  push  the  boat  with  the  sample  to  the  center  of  the  tube 
by  means  of  a  suitably  bent  wire  or  a  glass  rod,  stopper  the  tube 
and  make  a  test  to  see  if  the  apparatus  is  tight.  For  this  purpose 
first  open  the  stopcock  next  to  the  furnace  and  allow  oxygen  to 
pass  into  the  apparatus  until  no  more  bubbles  pass  through  the 
wash  bottle  from  the  gasometer.  If  the  apparatus  is  found  to  be 
tight  up  to  this  point,  open  the  next  stopcocks  in  the  tubes  of  the 
train,  one  by  one,  waiting  each  time  until  the  gas  bubbles  stop. 
Then,  if  the  connections  are  all  tight,  relieve  the  excess  oxygen 
pressure  by  opening  gradually  the  stopcock  in  the  front  end  of  the 
train.  Continue  passing  a  slow  stream  of  oxygen  through  the 
apparatus  and  begin  the  heating. 

In  working  with  a  Heraeus  furnace  of  50-mm.  internal  dia- 
meter, with  which  the  maximum  temperature  of  1,300°  is  given 
with  a  current  of  10.5  amperes  at  220  volts,  the  method  of  opera- 
tion is  as  follows : 

First,  have  all  the  resistance  in  the  electric  circuit.  Turn  on 
the  current  and  move  the  rheostat  arm  back  until  the  ammeter 
shows  9  amperes.  As  the  current  drops  1  or  2  amperes  cut  out 
more  resistance  and  keep  the  current  at  9  to  10  amperes. 

During  a  combustion  the  galvanometer  indicates  approxi- 
mately these  changes  in  temperature : 

after  5  min.  200°C. 
after  15  min.  650°C. 
after  30  min.  850 °C. 
after  45  min.  980°C. 
after  60  min  1,060°C. 
after  67  min.  1,100°C. 

The  combustion  usually  starts  at  a  temperature  between  850 
and  980°  and  is  indicated  by  a  sudden  slowing  up  of  the  gas  cur- 
rent in  the  last  wash  bottle  and  an  increase  in  the  rate  at  which 
the  oxygen  flows  through  the  first  wash  bottle.  To  prevent  the 
back  pressure  from  forcing  air  into  the  soda-lime  tubes,  increase 
the  supply  of  oxygen  while  the  sample  is  burning. 

Maintain  the  temperature  of  the  furnace  for  15  or  20  min. 
at  1,100°  or,  at  the  most,  1,200°,  and  continue  passing  a  slow 
stream  of  oxygen  through  the  apparatus. 

At  the  end  of  this  time  the  combustion  is  surely  ended.     Shut 


CARBON  43 

off  the  electric  current,  turn  the  lever  of  the  resistance  box  back 
and  pass  oxygen  through  the  tube  for  15  min.  longer,  to  drive 
all  of  the  carbon  dioxide  out  of  the  combustion  tube  and  drying 
tube.  Finally,  close  the  stopcocks  of  the  soda-lime  tubes,  re- 
move them  from  the  train  and  weigh  them  after  allowing  them  to 
stand  at  least  half  an  hour  in  the  balance  case.1  After  the  soda- 
lime  tubes  have  been  taken  off,  close  the  stopcock  from  the  oxygen 
tank  and  allow  the  furnace  to  cool. 

If  another  combustion  is  to  be  made  at  once,  weigh  out  the 
new  sample  while  the  furnace  is  cooling.  When  the  temperature 
has  fallen  to  about  600°  or  less,  pull  out  the  old  boat  with  a  hook 
made  of  clean  copper  wire.  Pass  oxygen  through  the  tube  for  5 
min.,  connect  the  weighed  soda-lime  tubes  and  push  the  new 
sample  into  the  tube.  Turn  on  the  electric  current  and  proceed 
as  before.  The  time  taken  to  bring  the  warm  tube  up  to  the  com- 
bustion temperature  is  much  less  now  and  less  current  is  used,  two 
factors  of  great  importance  where  work  is  being  done  on  a  large 
scale.  If  large  pieces  are  used  for  combustion  it  often  happens 
that  the  ferric  oxide  after  the  combustion  is  left  in  the  form  of 
loose  pieces  which  can  easily  be  removed  from  the  boat;  if  the 
material  is  finely  divided  the  mass  usually  fuses  to  the  boat. 

The  porcelain  boat  can  be  cleaned  for  use  a  second  time  by 
heating  it  for  a  long  time  with  concentrated  hydrochloric  acid  to 
remove  the  adhering  oxide.  This  hardly  pays,  however,  when 
the  price  of  unglazed  procelain  is  low. 

The  computation  of  the  carbon  content  is  the  same  as  in  the 
previous  method. 

ACCURACY  OF  THE  VALUES  FOUND  BY  THE  DIRECT  COMBUSTION 

METHOD 

The  weight  changes  in  the  soda-lime  tubes  in  the  blank  runs  are 
within  the  error  of  weighing.  Assuming  the  error  of  weighing 
to  be  not  greater  than  ±0.0005  g.,  the  percentage  errors  are: 

For  a  1-g.  sample  ±0.015  per  cent 
For  a  2-g.  sample  +0.007  per  cent 

1  This  leaves  oxygen  in  the  tubes  which  weighs  slightly  more  than  the  air 
they  originally  contained.  The  tubes  are  so  small,  and  there  is  so  little  free 
air  space  that  it  is  not  necessary  to  correct  for  this  slight  error.  If  the  initial 
weight  of  the  tubes  was  made  when  they  were  filled  with  oxygen,  this  error 
disappears. 


44  CHEMICAL  ANALYSTS  OF  METALS 

The  method  of  direct  combustion  in  oxygen  is,  therefore, 
slightly  more  exact  than  the  chrome-sulfuric  acid  method.  In 
this  case,  too,  the  errors  are  found  in  the  second  decimal  place  so 
that  if  small  weight  samples  are  taken  (1  to  3  g.)  the  allowable 
deviations  are  the  same  as  those  given  for  the  chrome-sulfuric 
acid  method  (p.  31). 

In  order  to  reduce  the  effect  of  the  weighing  error  and  so  get 
more  accurate  carbon  values,  a  larger  sample  may  be  taken 
(10  to  15  g.)  and  burned  in  a  larger  porcelain  boat  and  in  a  large 
tube. 

APPLICABILITY  OF  THE  METHOD 

All  the  metals  and  alloys  mentioned  under  the  chrome-sulfuric 
acid  method,  including  those  which  could  not  be  decomposed  by 
that  method,  will  be  decomposed  in  a  current  of  oxygen  at  tem- 
peratures between  1,100  to  1,200°. 

With  certain  substances,  like  ferro-vanadium  and  molybdenum 
which  give  readily  fusible  oxides  that  are  likely  to  injure  the 
combustion  tube,  it  is  advisable  to  place  the  sample  in  the  boat  on 
top  of  some  absorbent  material  such  as  ignited  alumina. 

DETERMINATION  OF  GRAPHITE  AND  TEMPER  CARBON 

Principle. — Graphite  and  temper  carbon  are  so  similar  in 
their  chemical  behavior  that  they  cannot  be  separated  by  ana- 
lytical methods.  The  precipitation  and  separation  of  combined 
carbon  is  based  on  the  fact  that  graphite  and  temper  carbon  are 
not  attacked  by  boiling  dilute  nitric  acid,  while  the  various  forms 
of  combined  carbon  form  volatile  compounds,  or  compounds 
soluble  in  nitric  acid. 

Procedure  (Ledebur). — With  dark  gray  cast  iron  use  1  g., 
with  light  gray  or  tempered  iron  2  to  5  g.,  and  with  high-nickel 
steel  use  5  to  10  g.  of  the  metal.1  Weigh  the  sample  into  a  300 
to  600-c.c.  beaker  and  heat  it  with  dilute  nitric  acid  (d.  1.2) 
using  about  25  c.c.  of  acid  for  each  gram  of  metal.  Immerse  the 
beaker  in  cold  water,  or  hold  it  under  the  tap,  to  prevent  too 

1  In  determining  graphite  or  temper  carbon  it  is  often  better  to  use  small 
pieces  rather  than  turnings.  This  is  especially  true  when  it  is  a  question 
of  determining  the  amount  of  graphite  or  temper  carbon  at  one  place  on  a 
specimen.  (See  Part  II.) 


CARBON  45 

violent  action  at  the  start  with  a  consequent  loss  of  material 
due  to  spattering.  After  the  action  has  slackened,  heat  the 
beaker  on  a  sand  bath,  or  over  an  asbestos  plate,  until  the  metal 
is  completely  dissolved.  If  the  sample  contains  much  silicon 
(e.g.,  gray  pig  iron)  add  J^  to  1  c.c.  of  hydrofluoric  acid1  to  dis- 
solve the  gelatinous  silicic  acid,  which  would  otherwise  clog  the 
pores  of  the  filter.  Take  care  not  to  let  any  particles  of  paraffin 
from  the  acid  container  drop  into  the  solution.  Cover  the 
beaker  with  a  watch-glass  and  boil  the  solution  very  gently,  over 
a  small  flame,  for  1  or  2  hr.  Then  dilute  with  water,  set  the 
beaker  aside  for  a  short  time  to  allow  the  insoluble  matter  to 
settle,  and  filter  through  a  well-fitting  asbestos  filter2  into  an 
Erlenmeyer  flask. 

After  the  liquid  and  residue  have  all  been  poured  out  of  the 
beaker,  rub  the  sides  of  the  glass  with  a  rubber-tipped  stirring- 
rod  to  remove  any  adhering  particles,  then  rinse  the  beaker  with 
hot  water  and  wash  the  filter  and  residue  until  free  from  acid. 

The  wet  residue  on  the  filter  may  be  used  at  once  if  the  carbon 
is  to  be  determined  by  the  Corleis  method.  Otherwise  it  should 
be  dried  at  110°,  transferred  to  a  combustion  boat  and.  analyzed 
by  any  of  the  methods  that  have  been  given  for  the  determination 
of  total  carbon. 

Instead  of  the  Ledebur  method,  the  following  treatment  is 
recommended  by  the  American  Society  for  Testing  Materials. 

Dissolve  the  sample  in  nitric  acid,  d.  1.13,  and  boil  the  solu- 

1  It  is  best  to  pour  the  hydrofluoric  acid  into  the  beaker  in  such  a  way 
that  it  will  not  come  into  immediate  contact  with  the  glass. 

2  Asbestos  for  this  purpose  is  prepared  as  follows:  Cut  long-fibered  asbestos 
into  pieces  about  1  cm.  long  and  heat  them  with  successive  portions  of  strong 
hydrochloric  acid,  until  a  portion  of  fresh  acid  is  not  colored  appreciably 
yellow.     Wash  the  asbestos  free  from  acid  with  hot  water,  dry  the  mat  of 
asbestos  in  the  hot  closet  and  finally  ignite  it  in  a  porcelain  crucible  to 
destroy  any  organic  matter. 

To  make  the  filter,  place  some  of  the  ignited  asbestos  in  the  stem  of  an 
ordinary  short  funnel.  By  a  stream  from  the  wash  bottle,  distribute  the 
fibers  in  such  a  way  that  the  fine  material  will  close  the  pores  made  by  the 
coarser  fibers  and  form  a  tight  mat. 

The  filter  is  known  to  be  tight  if  the  funnel  stem  will  stay  full  of  water. 
An  asbestos  filter  made  in  this  way  will  filter  rapidly  and  if  enough  asbestos 
is  used  will  be  tight  enough  to  hold  all  but  the  most  finely  divided  precipi- 
tates. Another  method  of  preparing  ignited  asbestos  is  given  on  page  34. 


46  CHEMICAL  ANALYSIS  OF  METALS 

tion  5  or  10  min.  to  expel  hydrocarbons.  Filter  the  residue  on 
ignited  asbestos  and  wash  several  times  with  hot,  dilute  caustic 
potash  solution,  d.  1.10,  then  with  dilute  hydrochloric  acid  and 
finally  with  hot  water.  Dry  at  110°  and  analyze  as  for  total 
carbon. 

COLORIMETRIC     METHOD     FOR    DETERMINING    CARBON   IN    STEEL 

Principle. — This  method,  suitable  only  for  routine  work, 
depends  upon  the  fact  that  the  color  produced  by  dissolving  steel 
in  nitric  acid  deepens  as  the  carbon  content  increases.  The 
color  produced  by  free  cementite  varies  somewhat  from  that 
produced  by  the  same  quantity  of  carbon  present  as  martensite 
and  on  boiling  the  solution  some  of  the  carbon  is  expelled  in  the 
form  of  hydrocarbons.  It  is  important,  therefore,  that  the  color 
should  be  compared  with  that  produced  by  the  same  weight  of  an 
analyzed  steel  containing  practically  the  same  amount  of  carbon 
and  with  the  carbon  in  the  same  metallographic  condition.  It 
is  necessary  to  use  a  series  of  steels  with  varying  carbon  contents 
as  standards.  The  standards  must  also  be  prepared  at  the  same 
time  under  exactly  the  same  conditions. 

Procedure. — Dissolve  0.2  to  0.5  g.  of  steel  in  a  test  tube  with 
5  to  20  c.c.  of  nitric  acid,  d.  1.24,  made  by  diluting  1,000  c.c.  of 
concentrated  acid,  d.  1.42,  with  1,200  c.c.  of  distilled  water.1 
Boil  gently  until  all  the  steel  is  dissolved.  Cool  and  compare 
with  standards  prepared  at  the  same  time. 

1  The  nitric  acid  is  approximately  7-normal. 


CHAPTER  III 
MANGANESE 

The  manganese  content  of  iron  and  steel  varies  considerably. 
In  ingot  iron  it  is  usually  very  low  and  in  ordinary  steel  it  rarely 
amounts  to  more  than  1  per  cent.  In  manganese  steel  and  in 
certain  other  special  steels,  however,  much  more  manganese  is 
present.  Certain  grades  of  cast  iron  contain  considerable  man- 
ganese and  in  ferro-manganese,  silico-manganese,  chrome-man- 
ganese, and  other  manganese  alloys,  this  element  constitutes 
the  most  important  constituent. 

To  the  analytical  chemist,  manganese  is  an  interesting  element 
because  there  are  so  many  characteristic  reactions  that  may  be 
used  for  its  qualitative  detection  and  quantitative  determination. 
There  are,  for  example,  a  number  of  manganese  compounds  easy 
to  prepare  which  are  so  insoluble  that  they  may  be  used  for 
gravimetric  methods.  Then  again,  manganese  compounds  in 
various  states  of  oxidation  are  known  and  favorite  volumetric 
methods  depend  upon  the  oxidizing  power  of  certain  of  these 
compounds.  Manganese  also  forms  highly  colored  compounds 
and  one  of  these  forms  the  basis  of  several  colorimetric  methods. 
Attempts  have  also  been  made  to  determine  manganese  electro- 
lytically  but  it  is  rather  difficult  to  maintain  conditions  such  that 
only  one  electrolytic  reaction  will  take  place;  it  is  easy  to  make 
permanganate  electrolytically  and  easy  to  deposit  manganese  as 
dioxide  upon  the  anode  but  it  is  difficult  to  make  one  of  these 
oxidation  reactions  take  place  quantitatively  without  any  of  the 
other  product  being  formed  at  the  same  time  so  that  electrolytic 
methods  for  determining  manganese  are  not  to  be  recommended. 

Personal  preferences  will  always  have  a  great  deal  to  do  with 
the  choice  of  the  method  used  for  determining  the  manganese 
content  of  iron  or  steel  and  also  with  regard  to  the  details  of 
carrying  out  the  method.  No  attempt  will  be  made  to  describe 
all  of  the  good  methods  but  typical  ones  will  be  chosen. 

47 


48  CHEMICAL  ANALYSIS  OF  METALS 

For  determining  small  quantities  of  manganese  the  most 
suitable  methods  are  those  which  depend  upon  the  formation  of 
permanganate.  This  may  be  accomplished  by  the  action  of 
sodium  bismuthate,  ammonium  persulfate  in  the  presence  of  a 
catalyzer,  or  by  lead  dioxide.  The  violet  color  of  permanganate 
can  be  obtained  by  any  of  the  above  reagents  under  suitable 
conditions  when  considerably  less  than  1  mg.  of  manganese  is 
present  in  the  solution.  If  the  quantity  of  manganese  is  very 
small,  a  colorimetric  method  is  suitable  but  with  higher  manga- 
nese content  it  is  better  to  find  out  how  much  permanganate  has 
been  formed  by  discharging  the  color  with  a  known  quantity  of 
a  reducing  agent  such  as  ferrous  salt  or  arsenite. 

Other  oxidizing  agents  convert  bivalent  manganous  ions, 
formed  by  dissolving  the  metal  in  acid,  into  insoluble  manganese 
dioxide.  The  precipitated  dioxide  may  be  analyzed  gravi- 
metrically  or  its  oxidizing  power  upon  a  solution  containing  a 
known  quantity  of  ferrous  salt  or  oxalate  may  be  determined. 
One  of  the  well-known  volumetric  methods  depends  upon  the 
fact  that  when  bivalent  manganese  ions  in  nearly  neutral  solution 
are  allowed  to  react  with  permanganate  ions,  all  of  the  man- 
ganese, both  of  the  sample  and  reagent,  can  be  converted  into 
insoluble  manganese  dioxide. 

Gravimetrically,  manganese  may  be  determined  accurately 
as  pyrophosphate,  Mn2P2O7,  as  sulfate,  MnSO4,  or  as  sulfide, 
MnS.  Of  these  last  compounds,  the  sulfate  is  soluble  in  water 
but  salts  of  acids  less  volatile  than  sulfuric  acid  may  be  easily 
changed  to  sulfate  in  a  weighed  crucible  or  dish  and  the  sulfate 
of  manganese  can  be  heated  gently  without  undergoing 
decomposition. 

All  oxides  of  manganese  are  converted  into  Mn304  upon  strong 
ignition,  and  manganese  is  often  determined  in  this  form. 

The  method  first  to  be  described  is  that  recommended  as 
standard  by  the  American  Society  for  Testing  Materials.  A.  A. 
Blair1  has  characterized  the  method  as  more  accurate  than  any 
other  method  known  to  him  and  Blum,2  working  at  the  Bureau  of 
Standards,  has  shown  that  it  can  be  used  even  with  materials 
rich  in  manganese. 

!«/.  Am.  Chem.  Soc.,  26,  793  (1904). 
2  Ibid.,  34,  1382  (1912). 


MANGANESE  49 

1.  DETERMINATION  OF  MANGANESE  BY  THE  B1SMUTHATE 

METHOD 

Principle. — When  sodium  bismuthate  is  added  to  a  cold  solu- 
tion of  manganous  salt,  containing  considerable  free  nitric  acid 
and  no  chloride  or  reducing  substance,  the  colorless  manganous 
cations  are  converted  into  purple  permanganate  anions: 

5BiC>7  +  2Mn+^4-  14H+  =  2MnO7  +  5Bi+++  +  7H20 

The  excess  of  the  reagent  is  insoluble  and  can  be  removed  by 
nitration  through  asbestos. 

The  permanganate  ions  on  being  treated  with  a  known  quan- 
tity of  suitable  reducing  agent  are  changed  back  to  manganous 
ions  and  the  excess  of  reducing  agent  is  determined  usually 
by  titration  with  standardized  permanganate  solution. 

Schneider1  originally  proposed  the  use  of  bismuth  tetroxide  as 
oxidizing  agent  and  titrated  the  permanganate  with  hydrogen 
peroxide  solution.  Reddrop  and  Ramage2  used  sodium  bis- 
muthate instead  of  the  tetroxide,  Bi2O4,  and  subsequently  Ibbot- 
son  and  Brearley3  replaced  the  hydrogen  peroxide  with  ferrous 
ammonium  sulfate.  To-day,  in  the  steel  laboratories  of  the 
United  States,  sodium  arsenite  is  commonly  used,  partly  because 
the  solution  is  more  stable ;  the  end-point  of  the  titration  is  less 
satisfactory  than  when  a  solution  of  a  ferrous  salt  is  used.4 

The  reaction  between  the  permanganate  and  the  various 
reducing  agents  may  be  expressed  as  follows: 

2Mn07  +  5H2O2  +  6H+  =  2Mn++  +  8H2O  +  502  t 

MnO4  +  5Fe++  +  8H+  =  5Fe+++  +  Mn++  +  4H2O 

2Mn07  +  5HAsO3~  -  +  6H+  <=>  2Mn++  +  5HAs07  ~  +  3H2O 

Reagents  Required. — 1.  Sodium  Bismuthate. — The  product 
sold  under  this  name  is  of  more  or  less  indefinite  composition 
but  corresponds  fairly  closely  to  the  formula  NaBiO3.  It  may 
be  prepared  by  heating  20  parts  of  caustic  soda  nearly  to  redness 
in  an  iron  or  nickel  crucible,  adding,  in  small  quantities  from 
time  to  time,  10  parts  of  dry,  basic  bismuth  nitrate,  followed  by 

1  Ding,  poly.,  J.,  269,  224. 

2  /.  Chem.  Soc.,  67,  268  (1895). 

3  Chem.  News,  84,  247  (1901). 

4c/..  KUHLING,  Ber.,  34,  404  (1901). 

4 


50  CHEMICAL  ANALYSIS  OF  METALS 

2  parts  of  sodium  peroxide  and  finally  pouring  the  brownish 
yellow  fused  mass  on  an  iron  plate  to  cool.  When  cold,  wash  the 
mass  four  or  five  times  by  decantation  with  water,  collect  on  an 
asbestos  filter  and  dry  at  100°.  The  compound  is  somewhat 
unstable  and  if  kept  over  6  months  it  should  be  tested  to  see 
if  its  oxidizing  power  is  still  sufficient.  Dark  brown  samples 
appear  to  be  just  as  efficient  as  those  which  are  yellow. 

2.  Nitric  Acid. — For  dissolving  the  sample,  use  nitric  acid 
(d.    1.13)    which  may   be    prepared    by   diluting    concentrated 
nitric  acid  (d.  1.42)  with  three  volumes  of  water.     This  acid, 
as  it  contains  25  per  cent  of  the  concentrated  acid  by  volume, 
will  be  called  the  25  per  cent  acid  (it  contains  about  22.5  per  cent 
of  anhydrous  HNO3  by  weight). 

For  diluting  the  solution  after  the  bismuthate  treatment  and 
for  washing  the  residue  on  the  filter,  use  3  per  cent  nitric  acid 
prepared  by  mixing  30  c.c.  of  nitric  acid,  d.  1.42  with  970  c.c. 
of  water.  All  the  nitric  acid  used  in  this  analysis  must  be  free 
from  nitrous  acid.  Since  Reynolds  and  Taylor1  have  shown  that 
nitric  acid  as  weak  as  10  per  cent  is  decomposed  by  light  and 
that  recombination  takes  place  in  the  dark,  the  bottles  of  con- 
centrated nitric  acid  and  of  25  per  cent  acid  should  be  preserved 
in  the  dark.  Nitrous  acid  reacts  with  permanganate  precipitat- 
ing manganese  dioxide,  so  that  if  nitrous  acid  is  present  in  the 
solution  treated  with  bismuthate,  some  of  the  manganese  may  be 
left  on  the  filter.  Moreover,  if  a  ferrous  salt  is  titrated  with 
permanganate  in  the  presence  of  nitric  acid  containing  some 
nitrous  acid,  an  excessive  amount  of  permanganate  will  be 
required. 

3.  Potassium   Permanganate    Solutions. — For    steels    contain- 
ing less  than   1   per  cent  of  manganese  0.037V  permanganate 
(0.95   g.    KMnO4   per  liter)  is  suitable;  for  higher  manganese 
content  a  0.1  N  permanganate  (3.16  g.  KMnC>4  per  liter)  should 
be  used.     The  addition  of  10  g.  caustic  potash  per  liter  lessens  the 
tendency  of  the  permanganate  solution  to  change  on  standing.2 
The   conditions  recommended   by  McBride3  for  standardizing 
tenth-normal  permanganate  against  sodium  oxalate  are  briefly 

i/.  Chem.  Soc.,  101,  131  (1912). 

2  BLUM,  /.  Am.  Chem.  Soc.,  34,  1379. 

a  J.  Am.  Chem.  Soc.,  34,  415  (1912). 


MANGANESE  51 

as  follows:  Volume,  250  c.c.;  acidity,  2  per  cent  concentrated 
sulfuric  acid  by  volume;  initial  temperature,  80  to  90°;  slow 
addition  of  permanganate  especially  at  the  beginning  and  end; 
final  temperature  not  less  than  60°;  end-point  correction  with 
a  blank  containing  a  known  amount  of  permanganate.  For 
standardizing  the  Q.03N  solution  not  more  than  0.075  to  0.1  g. 
of  sodium  oxalate  should  be  taken. 

4.  Ferrous  Sulfate  or  Ferrous  Ammonium  Sulfate  Solutions. — 
There  is  little  choice  between  these  substances  as  regards  the 
stability  of  their  solutions.     For  use  with  0.03JV  permanganate 
weight  out  12.4  g.  of  ferrous  ammonium  sulfate,  or  8.8  g.  of 
ferrous  sulfate  crystals,  add  50  c.c.  of  concentrated  sulfuric  acid 
and  dilute  to  1  liter.     For  use  with  0.17V  permanganate,  take 
39.2  g.  of  ferrous  ammonium  sulfate  or  27.8  of  ferrous  sulfate 
and  the  same  volumes  of  sulfuric  acid  and  water  as  before.     No 
appreciable  change  takes  place  in  the  ferrous  content  of  these 
solutions  during  a  period  of  a  few  hours.     The  0. 1 N  ferrous  solu- 
tions lose  about  1  per  cent  in  reducing  power  in  5  days.     The 
solutions  should  be  titrated  against  the  permanganate,  therefore, 
on  the  same  day  that  the  analyses  are  made. 

To  determine  the  reducing  power  of  the  ferrous  solutions,  take 
50  c.c.  of  25  per  cent  nitric  acid  and  add  a  little  sodium  bis- 
muthate.  Shake  and  allow  to  stand  a  few  minutes.  Dilute 
with  50  c.c.  of  3  per  cent  nitric  acid,  filter  through  an  asbestos 
filter  and  wash  with  100  c.c.  of  3  per  cent  nitric  acid.  To  the 
clear  filtrate  add  50  c.c.  of  ferrous  sulphate,  or  the  amount  to 
be  used  in  the  analysis,  and  titrate  at  once  with  permanganate 
to  the  first  visible  pink. 

The  treatment  with  bismuthate  is  not  absolutely  necessary 
but  it  affords  a  convenient  way  for  testing  the  efficacy  of  the 
filter. 

5.  Sodium  Arsenite  Solution. — Prepare  a  stock  solution  by 
heating  15  g.  of  arsenious  oxide,  As2O3,  and  45  g.  of  sodium 
carbonate  with  150  c.c.  of  distilled  water.     When  the  arsenic 
oxide  has  all  dissolved,  dilute  the  resulting  solution  of  sodium 
arsenite  to  a  volume  of  1  liter.     To  make  the  standard  solution 
of  sodium  arsenite,  dilute  300  c.c.  of  the  stock  solution  with 
700  c.c.  of  distilled  water  and  after  standardizing  against  the 
permanganate,  adjust  the  solution  so  that  it  is  0.0182-normal 


52  CHEMICAL  ANALYSIS  OF  METALS 

when  1  c.c.  of  solution  will  be  equivalent  to  0.100  per  cent  of 
manganese  on  the  basis  of  a  1-g.  sample  of  steel.  For  the  analysis 
of  ordinary  steels,  three  significant  figures  is  all  that  need  be 
considered  in  the  computation  and  the  sample  should  be  weighed 
to  the  nearest  centigram. 

Procedure  for  Steels. — Dissolve  1  g.  of  steel  in  50  c.c.  of  the 
25  per  cent  acid  using  a  200  to  300-c.c.  Erlenmeyer  flask.  When 
the  steel  has  all  dissolved,  boil  the  solution  gently  to  expel  oxides 
of  nitrogen.  Cool  somewhat  and  add  about  0.5  g.  of  sodium 
bismuthate  in  small  portions.  It  is  necessary  to  add  bismuthate 
until  a  permanent  permanganate  color  is  obtained  but  a  large 
excess  should  be  avoided. 

This  preliminary  oxidation  serves  to  oxidize  the  dissolved 
carbide  which  might  otherwise  react  with  the  permanganate 
after  it  is  formed. 

Heat  the  solution  for  a  few  minutes  until  the  pink  color  of 
permanganate  has  disappeared,  with  or  without  precipitation  of 
manganese  oxide.  Add  small  portions  of  ferrous  sulfate  (or  any 
other  suitable  reducing  agent  such  as  sulfurous  acid,  sodium 
sulfite,  or  hydrogen  peroxide)  to  the  hot  solution  in  sufficient 
quantity  to  dissolve  any  precipitated  manganese  dioxide,  but 
carefully  avoiding  an  excess  of  the  reagent.  Boil  the  solution 
for  2  min.  to  expel  oxides  of  nitrogen  and  cool  to  15°.  To  the 
cold  solution  add  a  slight  excess  of  sodium  bismuthate  (usually 
0.5  to  1.0  g.  is  sufficient;  an  excess  makes  the  subsequent  filtra- 
tion more  difficult)  and  agitate  well  for  at  least  J^  min.  Add 
50  c.c.  of  3  per  cent  nitric  acid,  washing  down  the  sides  of  the 
flask,  and  filter  through  an  alundum  crucible  or  asbestos  pad. 
Wash  the  residue  with  3  per  cent  nitric  acid,  using  50  to  100  c.c. 
and  making  sure  that  the  last  runnings  are  colorless.  A  suitable 
filter  may  be  made  by  tamping  down  a  wad  of  glass  wool  into 
an  ordinary  funnel  and  pouring  over  it  just  enough  suspended 
asbestos  fibers,  such  as  are  used  for  Gooch  crucibles,  to  form  a 
layer  sufficient  to  hold  back  the  excess  of  bismuthate.  If  too 
much  asbestos  is  used  the  filter  will  become  clogged  too  readily. 

Titrate  immediately  with  the  standard  sodium  arsenite  solu- 
tion, to  the  disappearance  of  the  pink  color.  Or,  as  many 
chemists  prefer,  add  enough  standard  ferrous  sulfate  solution  to 
decolorize  the  permanganate  (preferably  using  a  25  or  50-c.c. 


MANGANESE  53 

pipette)    and   titrate    the    excess  of  the  latter  with  standard 
permanganate. 

Procedure  for  Cast  Iron. — Dissolve  1  g.  of  metal  in  25  c.c.  of  25 
per  cent  nitric  acid  in  a  small  beaker.  When  all  action  has 
ceased,  filter  into  a  200-c.c.  Erlenmeyer  flask.  Wash  the  filter 
with  30  c.c.  of  the  25  per  cent  nitric  acid  and  proceed  as  with 
steels. 

The  removal  of  the  carbonaceous  residue  is  essential  as  other- 
wise it  is  almost  impossible  to  convert  all  the  manganese  to 
permanganate.  If  it  is  desired  to  test  an  insoluble  residue  for 
manganese,  volatilize  the  silica  by  treatment  with  sulfuric  and 
hydrofluoric  acids,  fuse  the  residue  with  a  little  potassium  pyro- 
sulfate  (potassium  acid  sulfate  heated  until  it  begins  to  fume), 
take  up  the  fusion  in  25  per  cent  nitric  acid,  and  then  treat 
with  sodium  bismuthate. 

In  the  analysis  of  white  irons,  it  may  be  necessary  to  treat 
the  solution  several  times  with  sodium  bismuthate  in  order  to 
destroy  all  the  iron  carbide  in  the  preliminary  treatment.  Other- 
wise, the  carbide  will  prevent  the  quantitative  conversion  of  the 
manganese  to  permanganate. 

Procedure  for  Ferro-manganese. — Treat  1  g.  with  25  per  cent 
nitric  acid  exactly  as  in  the  analysis  of  steel.  Dilute  the  solution 
to  500  c.c.  in  a  calibrated  flask  and  take  an  aliquot  part  corre- 
sponding to  from  0.01  to  0.02  g.  of  manganese.  Add  12  to  15  c.c. 
of  concentrated  nitric  acid  (d.  1.42),  dilute  to  50  or  60  c.c.,  and 
treat  with  sodium  bismuthate  in  the  usual  way. 

Procedure  for  Ferro-silicon. — Treat  1  g.  with  sulfuric  and 
hydrofluoric  acids  and  heat  until  thick  fumes  of  sulfuric  acid 
are  evolved.  Cool  and  dissolve  in  25  c.c.  of  25  per  cent  nitric 
acid.  Transfer  to  a  200-c.c.  flask,  rinse  the  dish  or  crucible  with 
25  c.c.  more  of  the  same  acid,  and  proceed  as  usual. 

Procedure  for  Special  Steels. — In  modern  alloy  steels,  particu- 
larly steels  used  for  self -hardening  or  high-speed  drills,  the 
element  chromium  is  likely  to  be  present  and  it,  like  manganese, 
is  easily  oxidized  by  sodium  bismuthate.  The  oxidation  of 
chromium  takes  place  more  slowly  than  that  of  manganese  and, 
to  effect  complete  oxidation,  it  is  desirable  to  work  at  the  boiling 
temperature,  in  which  case  the  manganese  is  changed  to  insoluble 
manganese  dioxide. 


54  CHEMICAL  ANALYSIS  OF  METALS 

During  the  preliminary  oxidation  in  the  above  directions,  some 
chromium  will  always  be  changed  to  chromate.  If  this  is  care- 
fully reduced  with  sulfurous  acid  or  sodium  sulfite,  and  the  solu- 
tion is  cooled  to  approximately  0°  in  ice  water,  agitation  with  a 
slight  excess  of  sodium  bismuthate  will  effect  the  complete  oxida- 
tion of  the  manganese  to  permanganate  and,  if  there  is  no  delay 
in  filtering  or  titrating,  correct  results  can  be  obtained  without 
any  appreciable  oxidation  of  chromium. 

Many  operators,  however,  find  trouble  when  chromium  is 
present  and  obtain  results  for  manganese  which  are  too  high.  To 
overcome  this  difficulty,  it  is  advisable  to  precipitate  the  chro- 
mium as  chromic  hydroxide  by  means  of  zinc  oxide  suspension1 
(20  g.  of  ZnO  triturated  to  a  paste  with  a  little  water  and  poured 
into  100  c.c.  of  distilled  water). 

Zinc  Oxide  Modification. — Weigh  2.50  g.  of  steel  into  a  300-c.c. 
casserole,  add  45  c.c.  of  6-normal  sulfuric  acid,  cover  the  casserole 
with  a  watch-glass  and  heat  until  the  steel  is  dissolved.  Add 
4  c.c.  of  concentrated  nitric  acid,  to  oxidize  the  iron2  and  evapo- 

1  C.  T.  Nesbitt  (Chem.  News.,  116,  64  (1917))  has  tested  a  number  of 
methods  for  determining   manganese   in   high-speed   steels  and   finds   the 
bismuthate  method  satisfactory  if  the  tungsten  is  completely  removed,  if 
the  chromium  is  carefully  reduced  and  if  the  titration  with  permanganate 
does  not  stop  until  an  end-point  is  permanent  for  5  min. 

Nesbitt  in  the  analysis  of  high-speed  steels  containing  chromium 
recommends  the  following  procedure:  Dissolve  1.10  g.  of  steel  in  12 
c.c.  of  concentrated  hydrochloric  acid.  Add  5  c.c.  of  concentrated  nitric 
acid  and  evaporate  to  sirupy  consistency.  Then  add  exactly  7  c.c.  of  con- 
centrated sulfuric  acid  and  wash  once  round  the  sides  of  the  beaker  with  a 
little  water.  A  thick  creamy  mass  forms  on  the  bottom  of  the  beaker. 
Leave  the  beaker  near  the  edge  of  the  hot  plate  for  20  min.  and  then  fume 
strongly  for  15  min.  to  make  sure  that  the  last  traces  of  chloride  are  removed. 
Cool,  take  up  with  30  c.c.  of  6-normal  nitric  acid  and  20  c.c.  of  water.  Boil 
and  filter  off  the  tungstic  acid  with  some  filter  paper  pulp  on  the  filter. 
Wash  the  filter  at  least  five  times  and  add  15  c.c.  of  concentrated  nitric 
acid  to  the  filtrate.  Add  a  pinch  of  sodium  bismuthate,  boil  and  carefully 
decolorize  with  sulfurous  acid.  Boil  off  the  excess  sulfurous  acid,  cool  to 
below  15°  and  continue  in  the  usual  way,  taking  care  that  there  is  no  delay 
after  the  final  addition  of  bismuthate. 

2  If  tungstic  acid  precipitates  from  the  solution  at  this  point  it  is  best  to 
remove  it.     After  the  addition  of  the  nitric  acid,  concentrate  to  a  small 
volume  and  dilute  with  60  c.c.  of  6-normal  nitric  acid.     Filter  off  the  pre- 
cipitate, using  filter  pulp  to  prevent  clogging  of  the  paper  filter.     Then 
proceed  with  the  neutralization  with  ZnO  in  the  usual  manner. 


MANGANESE  55 

rate  slowly  until  copious  fumes  of  sulfuric  acid  are  evolved. 
Cool,  add  100  c.c.  of  water  and  heat  until  the  sulfates  are  all 
dissolved.  Cool  and  transfer  the  solution  to  a  500-c.c.  calibrated 
flask.  Add  sodium  carbonate  solution  (60  g.  dissolved  in  about 
100  c.c.  of  water)  until  the  solution  is  nearly  neutral  and  the 
precipitated  hydroxides,  which  form  where  the  sodium  carbonate 
is  in  excess,  redissolve  very  slowly.  Then  add  small  portions  of 
the  zinc  oxide  suspension  until,  after  allowing  the  precipitate  to 
settle,  the  supernatant  liquid  is  practically  clear.  Cool  and 
make  up  to  the  mark  with  distilled  water.  Mix  thoroughly  by 
pouring  into  a  large  dry  beaker  and  back  again  into  the  flask, 
repeating  the  operation  several  times.  Allow  the  precipitate  of 
ferric  and  chromic  hydroxides  to  settle  and  then  filter  through  a 
dry  filter  transfer  200  c.c.  of  the  solution  (corresponding  to  1  g. 
of  steel)  by  a  pipette  or  graduated  flask  to  a  300-c.c.  Erlenmeyer 
flask,  add  25  c.c.  of  25  per  cent  nitric  acid  and  continue  as  in  the 
usual  bismuthate  method. 

Computation.  —  One  cubic  centimeter  of  normal  KMnO4soln.  = 
0.03161  g.  KMnO4  =  0.06700  g,  Na2C204  =  0.01099  g.  Mn.  If 
n  c.c.  of  KMn04  =  p  g.  of  Na2C2O4,  then  the  permanganate  is 

p  p  X  0.01099 

normal   and   X  C'C-  KMn°4   : 


>67  '-  n  X  0.067 

In  using  the  ferrous  sulf  ate  method,  subtract  the  number  of  cubic 
centimeters  of  KMnO4  used  in  the  analysis  from  the  cubic  centi- 
meters of  KMnO4  equivalent  to  all  the  ferrous  solution  used  and 
the  difference  gives  the  volume  of  KMnO4  solution  which  is 
equivalent  to  the  manganese  in  the  sample. 

With  the  sodium  arsenite  solution,  if  r  c.c.  KMnO4  =  r\  c.c.  of 

r  X  p  X  0.01099 
sodium  arsenite,  then  1  c.c.  Na2HAsO3  solution  =  -  —  -     ~  *„- 

g.  Mn.  If  s  represents  the  weight  of  sample,  n\  the  number  of 
cubic  centimeter  of  permanganate  used  in  titrating  the  excess 
of  ferrous  solution,  n2  the  number  of  cubic  centimeters  of  per- 
manganate equivalent  to  the  entire  quantity  of  ferrous  salt 
added,  and  T  the  value  of  1  c.c.  permanganate  in  terms  of 
Mn,  then 

(nt  -ni)TX  100  ,  ,  , 

—  -  =  per  cent  Mn 


56  CHEMICAL  ANALYSIS  OF  METALS 

Accuracy  of  the  Method. — When  the  conditions  are  right,  the 
bismuthate  process  is  certainly  as  accurate  as  any  known  method 
for  determining  manganese  in  solutions  containing  less  than  0.05 
g.  of  the  element.  In  the  analysis  of  samples  rich  in  manganese, 
satisfactory  results  are  obtained  by  using  an  aliquot  part  of  the 
original  solution.  Blum1  tested  the  method  in  four  ways: 
with  a  manganese  sulfate  solution  of  known  manganese  con- 
tent, by  reducing  a  measured  volume  of  permanganate  and  oxidiz- 
ing it  again  with  sodium  bismuthate,  by  analyzing  potassium 
permanganate  crystals  and  by  analyzing  a  standard  manganese 
ore.  Concordant  results  within  1  part  in  500  were  obtained. 
The  oxidation  of  the  manganese  to  permanganate  is  quantitative 
in  well-agitated  solutions  at  temperatures  below  25°  and  the 
acidity  of  the  solution,  when  the  bismuthate  is  added,  may  vary 
between  20  and  40  per  cent  in  a  volume  of  50  to  150  c.c.  The 
preliminary  treatment  with  sodium  bismuthate  should  never  be 
omitted  and  any  difficultly  soluble  residue  containing  oxidizable 
material  must  be  removed  by  filtration,  as  mentioned  in  the 
above  directions.  The  electrometric  titration  of  manganese  will 
be  described  in  Chap.  XX. 

2.  DETERMINATION  OF  MANGANESE  BY  THE  FORD-WILLIAMS 

METHOD 

This  method  depends  upon  the  precipitation  of  manganese 
dioxide  by  the  addition  of  potassium  chlorate  in  nitric  acid  solu- 
tion and  is  the  best  known  of  those  methods  which  separate  iron 
and  manganese  by  the  precipitation  of  the  latter.  In  England 
and  in  the  United  States  the  process  is  usually  attributed  to 
Williams2  or  to  Ford3  and  Williams  but  in  Germany  it  is  credited 
to  Hampe4  or  to  Beilstein  and  Jawein.  When  potassium  chlorate 
is  added  to  a  solution  containing  manganese  ions  in  the  presence 
of  strong  nitric  acid,  the  following  reaction  takes  place : 

Mn++  +  2C1O7  =  MnO2  +  2C1O2 
The  manganese  dioxide  is  obtained  as  a  precipitate  and   the 

1  Loc.  tit. 

2  Trans.  Inst.  Mining  Engineers,  10,  100. 

3  Ibid.,  9,  397. 

4  Chem.  Ztg.,  7,  73. 


MANGANESE  57 

chlorine  dioxide  is  boiled  off  as  a  gas.  The  precipitate  may  be 
dissolved  in  a  measured  volume  of  acid  ferrous  sulfate  solution 
or  hot  oxalic  acid  solution : 

MnO2  +  2Fe++  +  4H+  =  Mn++  +  2Fe+++  +  2H2O 
MnO2  +  4H+  +  C2Or~  =  Mn++  +  2CO2  +  2H20 

and  the  excess  of  reducing  agent  determined  by  titration  with 
permanganate. 

This  method,  like  the  bismuthate  method  already  described, 
is  recommended  by  the  American  Society  for  Testing  Materials 
for  the  determination  of  manganese  in  cast  iron.  It  is  capable 
of  giving  excellent  results  in  the  analysis  of  steels  although  not 
as  sensitive  as  the  bismuthate  method  for  determining  small 
quantities  of  manganese  and  not  as  reliable  as  the  Volhard 
method  for  determining  large  quantities  of  manganese. 

Solutions  Required. — Nitric  Acid. — For  dissolving  the  sample 
use  nitric  acid,  d.  1.42  diluted  with  an  equal  volume  of  water. 
This  acid  is  approximately  8-normal.  The  undiluted  acid  is 
always  understood  when  the  words  concentrated  nitric  acid  are 
used. 

Standard  Ferrous  Sulfate  Solution. — Dissolve  10  g.  of  pure 
FeSO.7H2O  in  900  c.c.  of  water  and  100  c.c.  of  concentrated  sul- 
furic  acid.  The  presence  of  the  sulfuric  acid  prevents  the 
precipitation  of  insoluble  basic  ferric  salt  which  will  otherwise 
form  when  the  solution  is  oxidized  by  dissolved  oxygen.  The 
solution  oxidizes  slowly  on  standing  and  must  be  standardized 
when  used. 

Standard  Permanganate,  about  0.03-normal.  Dissolve  about 
1  g.  of  permanganate  in  each  liter  of  water.  Allow  the  solution 
to  age  by  standing  some  days  or  by  boiling  it.1  Filter  through 
glass  wool  tamped  down  in  a  funnel  and  covered  with  a  thin 
layer  of  asbestos.  Use  the  first  runnings  to  rinse  out  the  care- 

1  If  the  permanganate  is  perfectly  pure  and  is  dissolved  in  water  that  has 
been  doubly  distilled,  the  last  time  with  permanganate  in  the  still,  the  solu- 
tion will  keep  indefinitely  if  protected  from  light  and  dust.  Ordinary 
distilled  water  contains  a  small  quanty  of  volatile  protein  which  reacts 
with  permanganate.  Reducing  gases  when  dissolved  in  water  have  the 
same  effect.  When  properly  aged  and  then  filtered  the  permanganate 
solution  is  very  stable.  When  it  once  begins  to  decompose  the  precipitated 
MnO2  acts  as  a  catalyzer  so  that  the  rate  of  decomposition  increases. 


58  CHEMICAL  ANALYSIS  OF  METALS 

fully  cleansed  stock  bottle.  To  standardize  the  solution,  weigh 
out  0.2  to  0.3  g.  of  pure  sodium  oxalate,  dissolve  in  250  c.c.  of 
water  containing  2  c.c.  of  concentrated  sulfuric  acid  and  heat  to 
about  90°.  Titrate  very  slowly  with  permanganate,  particularly 
at  the  beginning  and  end,  and  take  care  that  the  final  temperature 
is  not  less  than  50°.  The  values  of  1  c.c.  KMnO4  in  terms  of 
sodium  oxalate  should  agree  within  0.2  per  cent.  Since  the 
equivalent  weight  of  sodium  oxalate  is  67  (one-half  the  molecular 
weight)  the  normal  concentration  of  the  permanganate  is  found 
by  dividing  the  value  of  1  c.c.  in  terms  of  sodium  oxalate  by 
0.067. 

Procedure. — Dissolve  3  g.  of  the  sample  (weighed  to  the 
nearest  centigram)  in  40  c.c.  of  8-normal  nitric  acid.  In  the 
analysis  of  irons  filter  off  the  insoluble  residue  of  silica  and 
carbon.  Concentrate  the  solution  to  sirupy  consistency  in  a 
600-c.c.  Erlenmeyer  flask,  add  40  c.c.  of  concentrated  nitric  acid 
and  3  g.  of  potassium  chlorate  and  boil  the  solution  for  15  min. 
Remove  from  the  source  of  heat,  as  otherwise  C1O2  may  explode, 
add  15  c.c.  more  of  concentrated  nitric  acid,  another  3-g.  portion 
of  potassium  chlorate  and  boil  again  until  yellow  fumes  cease  to 
come  off.'  Cool  quickly,  by  placing  the  flask  in  cold  water  and 
rotating  the  contents,  and  filter  the  precipitated  manganese 
dioxide  on  asbestos.  A  satisfactory  filter  is  obtained  by  placing 
a  little  glass  wool  in  an  ordinary  funnel  and  pouring  on  it  a  little 
suspended  asbestos  fibers,  such  as  are  used  for  Gooch  crucibles. 
Wash  the  precipitate  with  concentrated  nitric  acid  till  free  from 
iron  and  with  water  till  free  from  acid.  Transfer  the  asbestos 
pad  and  precipitate  to  the  original  flask,  cover  with  50  c.c.  of 
standard  ferrous  sulfate  solution  and  dilute  with  water  to  a 
volume  of  200  c.c.  Shake  the  contents  of  the  flask  with  small 
pieces  of  glass  stirring-rod  to  break  up  the  precipitate,  until  the 
manganese  is  all  dissolved,  and  then  titrate  with  0.03-normal 
permanganate.  The  ferrous  sulfate  solution  must  be  standard- 
ized against  the  permanganate  solution  the  same  day  the  analysis 
is  made.  Measure  out  50  c.c.  of  the  solution,  dilute  to  200  c.c. 
and  titrate  with  permanganate. 

Computation. — If  a  c.c.  of  KMnO4  solution  react  with  p  g.  of 
pure  Na2C2O4,  if  50  c.c.  of  FeSO4  solution  react  with  b  c.c.  of 
KMnO4  and  if  c  c.c.  of  KMnO4  are  used  in  the  analysis  of  the 


MANGANESE  59 

solution  from  3  g.  of  metal  which  has  been  treated  with  50  c.c. 
of  FeSO4  soln.     Then 

p  X  1.099 


a  X  0.067  X 


-  Ib  —  c\  =  per  cent  Mn 


Accuracy  of  the  Method. — The  precipitate  formed  by  treat- 
ment with  potassium  chlorate  is  assumed  to  contain  all  the 
manganese  in  the  quadrivalent  condition.  This  is  probably  not 
strictly  true.  Moreover,  if  the  conditions  are  not  right,  often 
some  of  the  manganese  is  not  precipitated.  If  the  manganese 
dioxide  precipitate  stands  for  some  time  it  becomes  less  readily 
soluble  in  the  ferrous  sulfate  solution.  In  spite  of  these  objec- 
tions, however,  the  results  obtained  are  usually  satisfactory  and 
the  method  is  more  suitable  than  the  Volhard  method  for  steels 
containing  less  than  0.6  per  cent  manganese. 

3.  DETERMINATION  OF  MANGANESE  BY  THE  VOLHARD  METHOD 

This  method  has  always  been  a  favorite  one  in  Germany  and 
there  are  over  50  publications  concerning  it  in  scientific  journals 
since  1879. 

(A)  MODIFIED  VOLHARD  METHOD 

Principle. — Manganous  salts  react  with  permanganate  in 
accordance  with  the  following  equation : 

2Mn04-  +  3Mn++  +  2H20  =  5MnO2  +  4H+ 

Gorgeu1  first  attempted  to  use  this  reaction  as  a  basis  for  the 
volumetric  determination  of  manganese  but  Volhard  is  gener- 
ally considered  to  be  the  father  of  the  method  in  its  present 
form.2 

The  conditions  necessary  to  carry  out  the  reaction  strictly 
in  accordance  to  the  above  equation,  in  the  analysis  of  a  solution 
of  manganous  salt  containing  a  large  quantity  of  ferric  chloride, 
are  obtained  most  readily  by  precipitating  the  iron  from  a  hot, 
dilute  solution  with  a  slight  excess  of  zinc  oxide,  adding  quickly 
an  excess  of  potassium  permanganate,  and  titrating  the  excess 
of  the  latter  in  a  suitable  manner. 

1  Ann.  chim.  phys.,  Ill,  66,  154  (1862). 

2  DEISS,  Chem.  Ztg.,  34,  237  (1910). 


60  CHEMICAL  ANALYSIS  OF  METALS 

If  the  conditions  are  not  quite  right  it  is  possible  that  the 
reaction  between  the  manganous  salt  and  the  permanganate 
may  take  place  differently.  Thus,  for  example,  in  Wolff's1 
method  where  the  permanganate  is  added  gradually  after  the 
iron  has  been  precipitated  by  the  zinc  oxide,  less  permanganate 
is  required  to  precipitate  all  the  manganous  salt,  and,  within 
certain  limits,  the  volume  of  permanganate  required  is  smaller 
in  proportion  as  the  amount  of  zinc  oxide  added  is  large.  In 
some  cases  the  error  may  amount  to  10  per  cent  of  the  total 
manganese  content. 

If  the  zinc  oxide  excess  is  equal  to  zero,  so  that  only  ferric 
hydroxide  is  present  (a  condition  difficult  to  fulfil)  then  the  per- 
manganate consumption  by  the  Wolff  method  corresponds  to 
that  required  by  the  equation. 

The  reason  for  low  results  when  an  excess  of  zinc  oxide  is  used 
is  chiefly  due  to  the  fact  that  some  of  the  manganese  is  precipi- 
tated with  the  ferric  hydroxide. 

When  the  titration  of  the  manganous  salt  by  permanganate 
is  carried  out  in  a  slightly  acid  solution,  as  recommended  by 
Volhard,  the  results  are  lower  than  the  equation  demands. 
In  this  case  the  error  is  due  chiefly  to  the  fact  that  the  man- 
ganese dioxide  precipitate,  as  it  forms  slowly,  carries  with  it  some 
adsorbed  manganous  oxide  and  thereby  escapes  reaction  with  the 
permanganate. 

In  the  modification  suggested  by  Schoffel  and  Donnath,  the 
manganous  chloride  solution  containing  suspended  ferric  hy- 
droxide, formed  by  the  addition  of  an  excess  of  zinc  oxide,  is 
added  to  an  excess  of  permanganate  solution;  correct  results  may 
be  obtained  if  the  two  solutions  are  mixed  quickly  enough.  The 
condition  of  having  permanganate  always  present  in  excess  is 
not  alone  sufficient  to  prevent  disturbances  such  as  are  likely  to 
result  in  the  method  of  Volhard  and  Wolff. 

In  using  the  Wolff  method  it  is  often  proposed  to  avoid  error 
by  using  an  empirical  factor  for  the  permanganate  solution 
instead  of  the  theoretical  value  as  established  by  equations. 
Since,  however,  the  factor  varies  with  the  amount  of  zinc  oxide 
added  to  precipitate  the  iron,  it  is  evident  that  this  method  is 
not  altogether  satisfactory. 

lStahl  u.  Eisen,  1884,  702;  1891,  377. 


MANGANESE 


61 


Probably  the  most  successful  expedient,  and  one  that  gives 
good  results  in  the  hands  of  a  skilful  worker,  is  to  standardize 
the  permanganate  solution  against  a  manganous  solution  of 
known  content  in  exactly  the  same  way  in  which  the  analysis  is 
to  be  carried  out. 

Requisite  Apparatus  and  Solutions. — In  carrying  out  the 
titrations,  it  is  convenient  to  have  at  hand  a  wooden  frame, 
Fig.  12,  fitted  to  hold  in  an  inclined  position  two  flasks  of  1.1  to 
1.5  liters  capacity.  The  hollows  in  which  the  bottoms  of  the 
flasks  rest  are  covered  with  felt  to  prevent  breakage.  In  carrying 
out  a  titration,  the  frame  is  placed 
upon  the  working  bench  so  that  the 
middle  of  the  flask  is  at  about  on  a 
level  with  the  eye,  in  such  a  way  that 
there  is  a  background  of  a  window  on 
which  the  sun  is  not  shining. 

For  the  titration,  the  following  solu- 
tions are  used: 

1.  Potassium  Permanganate  Solu- 
tions.— It  is  well  to  have  two  solutions 
of  permanganate  on  hand,  a  weaker 

solution  containing  about  16  g.  of  potassium  permanganate  in  5 
liters  of  water  and  a  stronger  one  containing  about  40  g.  of  the 
permanganate  in  the  same  volume  of  solution. 

The  solutions  are  prepared  by  dissolving  weighed  portions  of 
pure  potassium  permanganate  in  a  beaker  using  distilled  water 
that  has  been  recently  boiled  and  allowed  to  cool.1  The  solu- 
tion is  decanted  off  from  time  to  time  into  a  clean  5-liter  flask 
and  eventually  diluted  up  to  the  mark.  Before  using  them  for 
titrations,  the  permanganate  solutions  should  stand  in  stoppered 
bottles  for  from  8  to  14  days,  protected  from  light  and  dust. 
At  the  end  of  this  time  any  oxidizable  matter  in  the  solution 
will  have  reacted  with  the  permanganate  and  any  manganese 
dioxide  present  as  colloid  in  the  freshly  prepared  solutions 
will  have  deposited  on  the  bottom  or  sides  of  the  bottle  in  the 
form  of  a  brown  precipitate.  The  solutions  should  then  be 

1  The  addition  of  10  g.  caustic  potash  per  liter  retards  the  decomposition 
of  permanganate  by  dust,  reducing  gases,  or  precipitated  manganese  dioxide. 
BLUM,  W.,  J.  Am.  Chem.  Soc.,  34,  1379. 


FIG.  12. 


62  CHEMICAL  ANALYSIS  OF  METALS 

filtered  through  asbestos.  If  protected  from  light  and  dust 
(filtering  the  air  entering  the  bottle  through  alkaline  permanga- 
nate) the  filtered  solution  will  keep  indefinitely.1 

2.  Sodium  Ar  senile  Solutions.  —  The  strength  of  two  arsenite 
solutions  are  chosen  preferably  so  that  1  c.c.  of  permanganate  is 
equivalent  to  about  2  c.c.  of  arsenite.  To  prepare  the  weak  and 
strong  solutions,  weigh  portions  of  8  and  20  g.  of  pure  arsenic 
trioxide  into  beakers  containing  half  as  much  pure  sodium 
hydroxide.  Dissolve  in  a  little  water,  with  heating,  filter  if 
necessary,  and  dilute  each  solution  to  a  volume  of  5  liters. 

STANDARDIZATION  OF  THE  PERMANGANATE  SOLUTIONS 

(a)  Against  Sodium  Oxalale.  —  Standardize  as  described  on 
page  50  using  about  0.3  g.  of  oxalate  for  the  weaker  solution 
and  0.8  g.  for  the  stronger  solution.  The  reaction  that  takes 
place  in  the  titration  may  be  expressed  as  follows: 

2Mn04~  +  5C2O4~~  +  16H+  =  2Mn++  +  10CO2  +  8H2O 

Thus,  2  molecules  of  permanganate  will  oxidize  5  molecules 
of  oxalate  and  we  have  seen  that  2  molecules  of  permanga- 
nate oxidize  3  molecules  of  manganous  salt  to  manganese  dioxide. 
Five  molecules  of  sodium  oxalate  (670.0  g.)  are  equivalent, 
therefore,  to  3  molecules  of  manganous  salt  (164.79  g.  of 
manganese.) 

If  a  g.  of  sodium  oxalate  require  n  c.c.  of  permanganate,  then 


1  c.c.  KMn04  soln.  =         '     *  ^  =  0.2460  ^  g.  Mn 


This  factor  applies  only  to  the  Volhard  method.2 

(b)  Against  Sodium  Thiosulfale  Solution.  —  When  potassium 
permanganate  is  added  to  an  acid  solution  of  potassium  iodide, 
the  following  reaction  takes  place: 

2MnO4~  +  101"  +  16H+  =  2Mn++  +  8H2O  +  5I2 
and   the  free  iodine  may  be  titrated  with  sodium  thiosulfate. 
I2  +  2S203"  =  21-  +  S406- 

1  cf.  MORSE,  HOPKINS  and  WALKER,  Am.  Chem.  J.,  18,  401;  GARDNER  and 
NORTH,  «/.  Soc.  Chem.  Ind.,  23,  599;  WARYNSKI  and  TSCHEISCHWILI,  J. 
chim.  phys.,  6,  567;  TREADWELL-HALL,   "Quantitative  Analysis,"  II,  603 
(1914). 

2  Ann.,  198,  333,  242,  98  (Volhard). 


MANGANESE  63 

If  the  strength  of  either  the  permanganate  or  of  the  thiosul- 
fate  solution  is  known,  that  of  the  other  solution  may  be  com- 
puted.1 The  reaction  furnishes  a  rapid  and  accurate  method  of 
standardization. 

Dissolve  about  2  g.  of  pure  potassium  iodide  in  300  c.c.  of 
water,  add  5  c.c.  of  dilute  hydrochloric  acid  (d.  1.12)  and  if 
the  solution  is  at  all  yellow  (free  iodine  liberated  by  iodate  in 
the  iodide  or  of  free  chlorine  in  the  acid)  carefu^y  discharge  the 
color  by  the  addition  of  a  drop  or  more  of  dilute  thiosulfate 
solution.  Add  to  the  colorless  solution  of  potassium  iodide  an 
accurately  measured  volume  of  the  permanganate  solution,  using 
50  c.c.  in  the  case  of  the  weaker  solution  and  25  to  30  c.c.  of  the 
stronger.  The  solution  is  at  once  colored  red  by  the  liberated 
iodine.2  In  case  a  precipitate  of  manganese  dioxide  is  formed, 
dissolve  it  by  the  addition  of  a  little  more  hydrochloric  acid. 
Titrate  the  solution  with  tenth-normal  sodium  thiosulfate  until 
nearly  colorless,  than  add  a  little  starch  solution3  and  finish  the 
titration. 

Computation. — The  above  equations  show  that  2  molecules 
of  permanganate  liberate  10  atoms  of  iodine  which  in  turn  react 
with  10  molecules  of  thiosulfate.  In  the  titration  of  the  man- 
ganous  salt  by  permanganate,  we  have  seen  that  2  molecules  of 
permanganate  react  with  3  molecules  of  manganous  salt.  Thus, 
3  atoms  of  manganese  in  the  bivalent  condition  have  the  same 
reducing  power  as  10  molecules  of  thiosulfate  and  1  c.c.  of  tenth- 
normal  thiosulfate  is  equivalent  to  in  y  IQAQ  =  0-3  X  0.05493  =; 

0.001648  g.  Mn.  If,  in  the  standardization,  n  c.c.  of  tenth-nor- 
mal thiosulfate  are  equivalent  to  a  c.c.  of  permanganate. 

1  c.c.  KMnO4  solution  =  0.001648  -  g.  Mn 

1  It  is   possible   to   prepare   perfectly   pure,    anhydrous   thiosulfate   (cf. 
YOUNG,  J.  Am.  Chem.  Soc.,  26,  1028)  and  with  this  salt  it  is  easy  to  prepare 
a  tenth-normal  solution. 

2  The  iodine  really  unites  with  unchanged  iodide  ions  to  form  Ii~  ions 
in  which  two-thirds  of  the  iodine  behaves  like  free  iodine. 

3  Zinc-iodide-starch  solution  can  be  bought  which  is  suitable  for  such 
titrations  or  a  starch  solution  may  be  prepared  by  dissolving  0.5  g.  of 
soluble  starch  in  25  c.c.  of  hot  water. 


64  CHEMICAL  ANALYSIS  OF  METALS 

The  results  obtained  by  this  method  of  standardization  agree 
closely  with  those  obtained  by  standardizing  against  sodium 
oxalate.  There  is  little  choice  between  the  two  methods.  The 
standardization  of  the  arsenite  solutions  is  explained  in  the  de- 
scription of  the  method  of  analysis. 

METHOD  OF  CARRYING  OUT  THE  ANALYSIS 

(a)  Preparation  of  the  Sample  for  the  Titration. — If  the  man- 
ganese alone  is  to  be  determined  in  an  alloy  containing  less  than 
10  per  cent  of  this  element,  proceed  in  the  following  manner: 

Weigh  out  three  separate  portions,1  each  containing  2  g.  of 
material,  into  a  porcelain  dish  of  12  cm.  diameter.  Cover  the 
dish  with  a  watch-glass  and  dissolve  each  sample  by  the  gradual 
addition  of  25  c.c.  of  nitric  acid  (d.  1.2).  When  solution  is 
complete,  remove  the  watch-glass,  evaporate  to  dryness,  and 
destroy  the  nitrates  by  igniting  at  first  over  asbestos  and  finally 
over  the  free  flame  until  no  more  nitrous  fumes  are  evolved. 
Cool  -and  take  up  the  residue  in  about  20  c.c.  of  concentrated 
hydrochloric  acid  (d.  1.2). 

If  a  dark-colored  residue  (containing  graphite)  remains  un- 
dissolved,  evaporate  the  hydrochloric  acid  solution  to  dryness, 
dehydrate  any  silicic  acid  by  heating  to  125°,  redissolve  in  hy- 
drochloric acid,  dilute,  filter  and  wash  the  residue  thoroughly  be- 
fore proceeding  with  the  titration.  The  undivided  solution  is 
used. 

If  graphite  is  not  present,  it  is  unnecessary  to  filter  off  the 
silica.  Evaporate  the  hydrochloric  acid  solution  of  the  oxides  to 
dryness,  to  remove  any  chlorine  that  may  have  been  formed  from 
the  interaction  of  manganomanganic  oxide  and  hydrochloric 
acid,  take  up  the  residue  in  hydrochloric  acid  (d.  1.12)  and 
rinse  the  solution  into  an  Erlenmeyer  flask  of  about  1  liter 
capacity.  The  solution  is  now  ready  for  titration. 

If  it  is  desired  to  combine  the  manganese  determination  with 
the  determination  of  silicon,  or  phosphorus  in  samples  rich  in 
phosphorus,  or  nickel  in  a  nickel  steel,  a  larger  quantity  of 
material  may  be  taken  for  the  analysis  and  an  aliquot  part  of 

1  One  sample  is  to  be  used  for  a  preliminary  titration  which  does  not,  as 
a  rule,  give  exact  results. 


MANGANESE  65 

the  solution  used  for  the  manganese  determination.  In  this  way 
a  better  average  sample  is  obtained.  Of  materials  containing 
up  to  10  per  cent  manganese,  from  8  to  10  g.  are  taken,  of  richer 
manganese  alloys  (ferro-manganese,  metallic  manganese,  etc.) 
a  correspondingly  smaller  amount  (down  to  2  g.).  Dissolve 
the  sample  in  nitric  acid  (d.  1.2)  and  remove  the  silica  as 
described  on  p.  64. 

Catch  the  filtrate  from  the  silica  in  a  500-c.c.  calibrated  flask, 
or,  if  the  weight  taken  was  less  than  8  or  10  g.,  in  a  250-c.c.  flask. 
If  a  dark-colored  residue  remains  after  volatilization  of  the  silicon 
by  treatment  with  sulfuric  and  hydrofluoric  acids,  dissolve  it 
in  the  crucible  with  a  little  hydrochloric  acid  (d.  1.12)  and  rinse 
the  solution  into  the  calibrated  flask. 

Fill  the  flask  up  to  the  mark  with  water  which  is  at  the  labora- 
tory temperature,  thoroughly  mix  by  pouring  back  and  forth 
into  a  dry  beaker  several  times,  and  take  an  aliquot  part  for 
the  manganese  determination  by  means  of  a  pipette,  a  smaller 
calibrated  flask,  or  by  weighing. 

If  the  substance  for  analysis  is  insoluble  in  acids,  ignite  from 
2  to  3  g.  with  magnesia  and  sodium  carbonate  as  described  for 
the  determination  of  silicon,  p.  124.  Transfer  the  ignited  mass 
from  the  crucible  to  an  agate  mortar,  moisten  with  water,  break 
up  the  larger  pieces  with  the  pestle  and  grind  into  a  fine  powder. 
Rinse  the  mass  into  a  beaker,  cover  the  latter  with  a  watch-glass 
and  add  a  little  sodium  peroxide  to  decompose  any  manganate 
that  was  formed  during  the  ignition.  Heat  the  liquid  on  the 
water  bath,  with  frequent  stirring,  until  the  excess  of  peroxide  is 
decomposed  and,  if  the  solution  then  appears  green  or  violet 
(from  manganate  or  permanganate),  repeat  the  treatment  with 
sodium  peroxide.  After  the  manganate  has  all  been  reduced, 
the  solution  should  be  colorless,  or  yellow  in  case  chromium  is 
present.  Filter  off  the  precipitate,  containing  all  the  manganese 
and  iron  together  with  the  magnesia,  etc.,  and  wash  it  well  with 
hot  water.  Rinse  the  precipitate  into  a  porcelain  dish  and  dis- 
solve it  in  hydrochloric  acid  (d.  1.12).  Evaporate  the  solu- 
tion nearly  to  dryness,  to  make  sure  that  all  the  chlorine  is 
expelled,  and  rinse  with  dilute  hydrochloric  acid  into  a  250-c.c. 
calibrated  flask.  Make  up  to  the  mark  with  water  and  take  an 
aliquot  part  for  the  titration. 


66  CHEMICAL  ANALYSIS  OF  METALS 

The  quantity  of  manganese  to  be  titrated  determines  which 
of  the  two  permanganate  solutions  should  be  used.  In  general, 
solutions  containing  from  40  to  80  mg.  of  manganese  (correspond- 
ing to  a  2-g.  sample  with  2  to  4  per  cent  manganese)  may  be 
titrated  with  the  weaker  solution;  if  the  manganese  content  is 
higher  the  stronger  solution  should  be  used. 

If  the  sample  contained  only  a  little  iron,  add  enough  pure  ferric 
chloride  to  each  solution  before  titration  so  that  the  iron  content 
will  correspond  to  about  1  g.  of  metal.  For  this  purpose,  it  is 
well  to  have  at  hand  a  solution  of  ferric  chloride  made  by  dis- 
solving about  500  g.  of  pure  ferric  chloride  (FeCl3  +  6H2O)  in 
water  with  a  little  hydrochloric  acid  and  diluting  to  1  liter;  such 
a  solution  contains  about  1  g.  of  iron  in  10  c.c. 

(6)  Titration  of  the  Solution. — The  solution  to  be  titrated, 
prepared  as  just  described,  should  be  in  an  Erlenmeyer  flask  of 
about  1  liter  capacity.  To  oxidize  traces  of  ferrous  salt  that 
may  be  present,  add  a  small  crystal  of  potassium  chlorate  or, 
better,  a  few  drops  of  pure,  concentrated  hydrogen  peroxide 
solution1  and  boil  gently  for  10  or  15  min.  to  destroy  the  excess 
of  oxidizing  agent  (replacing  the  hydrochloric  acid  lost  by 
evaporation).  There  should  be  no  odor  of  free  chlorine. 

Meanwhile  heat  the  distilled  water  necessary  for  the  titra- 
tion to  boiling  in  a  2-liter  flask  and  triturate  the  zinc  oxide 
necessary  for  the  precipitation  of  the  iron  in  a  mortar  with  water, 
until  a  thin  paste  is  obtained.  This  may  be  kept  in  a  small 
Erlenmeyer  flask.  If  the  approximate  manganese  content  of 
the  solution  is  not  known,  determine  it  by  a  trial  titration  carried 
out  in  the  following  manner: 

Dilute  the  manganese  solution  in  the  Erlenmeyer  flask  with 
boiling  water  until  the  volume  is  about  600  to  700  c.c.  Add 
the  suspension  of  zinc  oxide  in  small  amounts  until,  after  vigor- 
ous shaking,  all  the  iron  is  precipitated  in  the  form  of  brown 
ferric  hydroxide2  and  the  solution  is  clear  and  colorless  after  the 
precipitate  settles. 

1  Perhydrol. 

2  It  is  not  necessary  to  add  zinc  oxide  until  the  excess  whitens  the  pre- 
cipitate.    There  is  no  danger  of  an  excess  of  zinc  oxide  doing  any  harm, 
however,  provided  the  permanganate  solution  is  added  rapidly,  as  in  the 
main  analysis. 


MANGANESE  67 

For  convenience,  place  the  flask  in  an  inclined  position  in  the 
support  described  on  p.  61  while  the  precipitate  is  settling. 
Add  10  c.c.  of  the  permanganate  solution  from  a  burette,  shake 
vigorously  and  replace  the  flask  upon  the  support.  If,  when  the 
precipitate  settles,  the  supernatant  liquid  is  uncolored  by  per- 
manganate, add  another  10  c.c.  of  permanganate,  shake  and  again 
allow  to  settle.  Repeat  the  operation  until  the  solution  above 
the  precipitate  is  colored  by  permanganate.  Then  add  the 
corresponding  arsenite  solution  in  small  quantities,  shaking  and 
allowing  to  settle  after  each  addition.  Continue  to  add  arsenite 
solution  until  the  permanganate  is  decolorized. 

From  the  volumes  of  permanganate  and  arsenite  solutions 
used  in  this  trial  titration,  the  approximate  volume  of  perman- 
ganate required  can  be  computed  by  assuming  the  two  solutions 
to  be  of  the  same  strength.  The  exact  value  of  the  arsenite 
solution  is  determined  at  the  time  the  accurate  titration  is  made. 

For  this  accurate  titration  of  the  manganese  content  of  the 
solution,  measure  from  a  burette,  into  a  small  beaker,  from  2  to 
4  c.c.  of  permanganate  more  than  that  found  necessary  by  the 
trial  titration.  Then  dilute  the  manganese  solution  containing 
ferric  iron  to  a  volume  of  600  to  700  c.c.,  add  the  necessary 
quantity  of  zinc  oxide  suspension,  and  shake  well.  When  all  the 
iron  is  precipitated,  quickly  add  the  permanganate  solution  from 
the  beaker,  rinse  the  beaker,  and  shake  the  contents  of  the  flask 
vigorously. 

If  the  solution  should  now  be  colorless,  or  show  only  a  very  pale 
permanganate  color,  it  is  best  to  repeat  the  experiment  using  a 
somewhat  larger  quantity  of  permanganate. 

To  determine  the  excess  of  permanganate,  add  the  arsenite 
solution  in  small  portions  from  a  burette,  shaking  and  allowing 
to  settle  each  time,  until  the  supernatant  solution  is  colorless. 
It  is  necessary,  toward  the  last,  to  add  but  a  drop  or  two  of  arsen- 
ite solution  at  a  time. 

To  determine  the  reducing  action  of  the  arsenite  under  as 
nearly  as  possible  the  same  conditions,  add  5  c.c.  of  permanganate 
from  a  burette  to  the  hot  solution  that  has  just  been  titrated,  and 
again  titrate  with  arsenite  solution  until  the  permanganate  is  all 
decolorized.  In  this  way  the  value  of  1  c.c.  of  arsenite  solution 
in  a  cubic  centimeter  of  permanganate  is  determined,  and  the 


68  CHEMICAL  ANALYSIS  OF  METALS 

exact  volume  of  permanganate  required  to  react  with  the  man- 
ganese in  the  analyzed  sample  can  be  computed. 

If  ferric  chloride  solution  was  added,  then  an  equally  large 
volume  of  it  should  be  diluted  with  hot  water,  treated  with  zinc 
oxide  suspension  and  titrated  with  permanganate  until  a  pink 
color  is  obtained.  The  volume  of  permanganate  used  here 
should  be  deducted  from  that  used  in  the  main  experiment. 

Computation. — Let  s  represent  the  weight  of  sample,  ax,  the 
number  of  cubic  centimeters  of  permanganate  used  in  the  main 
titration,  61,  the  number  of  cubic  centimeters  of  arsenite  solution 
used  in  the  main  titration,  a2  the  number  of  cubic  centimeters  of 
permanganate  added  afterward,  &2the  number  of  cubic  centimeters 
of  arsenite  required  to  react  with  this  last  permanganate,  c  the 
number  of  cubic  centimeters  of  permanganate  required  by  the 
ferric  chloride  solution  if  any  were  used,  and  T  the  value  of  1 
c.c.  of  permanganate  solution  in  terms  of  metallic  manganese. 
Then: 

[ai  -  61—   -  c]  X  T  X  100 

=  per  cent  Mn 

s 

Test  Analyses. — The  method  has  been  tested  by  taking  an 
accurately  measured  volume  of  permanganate  solution,1  reducing 
it  by  evaporation  with  hydrochloric  acid,  and  then  titrating  with 
the  addition  of  ferric  chloride  solution  in  exactly  the  same  way 
as  in  any  analysis.  The  results  show  that  the  reaction  takes 
place  strictly  in  accordance  with  the  equation  given  when  the 
above-described  method  is  used. 

Purity  of  the  Zinc  Oxide. — Each  new  lot  of  zinc  oxide  should 
be  tested  to  see  if  it  is  sufficiently  pure.  Dilute  10  c.c.  of  ferric 
chloride  solution  with  hot  water  to  a  volume  of  about  600  c.c., 
add  4  g.  of  zinc  oxide  which  has  been  rubbed  into  a  paste  with 
water,  and  titrate  with  permanganate.  Repeat  the  experiment 
with  10  c.c.  of  ferric  chloride  solution,  15  c.c.  of  hydrochloric  acid 
(d.  1.12)  and  10  g.  of  zinc  oxide.  If  the  zinc  oxide  is  pure  the 
permanganate  consumption  will  not  be  greater  in  the  second  case 
than  in  the  first. , 

1  cf.  WOLFF,  Stahl  u.  Eisen,  11,  380;  DE  KONINCK,  Bull.  soc.  chim.  Belgique, 
18,  56. 


MANGANESE  69 

ACCURACY  OF  RESULTS  OBTAINED  BY  THE  MODIFIED  VOLHARD 

METHOD 

The  manganese  content  of  a  solution  containing  manganous 
salt  and  ferric  chloride  may  be  determined  within  a  fraction  of  a 
milligram.  Too  high  values  are  often  obtained  when  the  solu- 
tions contain  substances  other  than  manganous  salt  which  can 
react  with  permanganate. 

Such  substances  are  chromium,  cobalt  and  vanadium.  In 
the  analysis  of  most  kinds  of  ordinary  steel  these  elements  are 
present  only  to  an  inappreciable  extent. 

Repeated  determinations  of  chromium  in  ordinary  grades  of 
iron  and  steel  to  which  no  chromium  was  intentionally  added, 
have  shown  that  chromium  in  small  amounts  is  likely  to  be  pres- 
ent and  as  a  result  the  Volhard  method  is  likely  to  give  too  high 
values.  This,  together  with  the  difficulty  in  obtaining  the  correct 
end-point  make  the  method  less  suitable  for  the  determination 
of  quantities  of  manganese  less  than  1  per  cent  than  either  of 
the  other  volumetric  methods  to  be  described. 

Usually  it  is  possible  to  obtain  duplicate  determinations  that 
agree  within  the  following  limits: 

Manganese  content  Permissible  deviation 

1  to  2  per  cent  0.04  per  cent 

2  to  10  per  cent  0.06  per  cent 
10  upwards                                         0 . 1  per  cent 

It  is  difficult  to  get  good  results  by  this  method  in  the  analy- 
sis of  nickel  steels.  This  is  partly  because  the  yellowish  green 
color  of  nickel  solution  and  the  violet  of  permanganate  are 
complimentary  colors  and  at  the  right  concentration  give  a 
colorless  solution.  The  chief  trouble,  however,  is  due  to  the 
small  quantity  of  cobalt  which  is  usually  present.  Cobaltous 
salts  are  oxidized  by  permanganate  with  the  formation  of  in- 
soluble cobaltic  oxide. 

4.  DETERMINATION     OF     MANGANESE    BY    THE    PERSULFATE 

METHOD1 

In  a  boiling  solution  of  a  manganous  salt,  ammonium  persul- 
fate  converts  all  the  manganese  to  permanganate  if  a  small 

lcf.  WALTERS,  Proc.  Eng.  Soc,  Western  Penna.,  17,  257  (1901);  Chem. 
News,  84,  239. 


70  CHEMICAL  ANALYSIS  OF  METALS 

amount  of  dissolved  silver  salt  is  present  as  catalyzer.  In 
the  absence  of  the  catalyzer  all  the  manganese  is  precipitated 
as  dioxide.  A  number  of  methods  have  been  worked  out  on 
the  basis  of  each  of  these  reactions. 

The  American  Society  for  Testing  Materials  recommends  the 
method  to  be  described,  which  depends  upon  the  formation  of 
permanganate,  for  routine  work  in  the  analysis  of  steel.  The 
method  is  not  as  reliable  as  the  bismuthate  method.  There 
is  some  difficulty  in  getting  ammonium  persulfate  of  suitable 
purity  and  permanganate  is  not  very  stable  in  a  hot  solution 
but  the  excess  of  reagent  is  decomposed  by  boiling  the  solution 
and  does  not  have  to  be  filtered  off  as  in  the  bismuthate  process. 
This  results  in  a  saving  of  time. 

The  reaction  of  oxidation  may  be  expressed  as  follows: 

2Mn++  +  5S208—  +  8H2O-»2MnO4-  +  10SO4"  +  16H+ 
2H2O  +  2S2O8-~-*4S04~~  +  4H+  +  O2  T 

The  reaction  of  titration  is  the  same  as  in  the  bismuthate 
method. 

Procedure. — Dissolve  0.1  to  0.3  g.  of  steel  in  15  c.c.  of  25 
per  cent  nitric  acid  (see  Bismuthate  method)  in  a  small  Erlen- 
meyer  flask  or  large  test  tube.  Boil  gently  until  the  solution  is 
complete  and  the  liquid  is  clear.  Add  15  c.c.  of  0.08-normal 
silver  nitrate  solution  (1.33  g.  of  silver  nitrate  per  liter)  and  1  g. 
of  ammonium  persulfate  and  continue  heating  for  %  min.  after 
the  oxidation  begins  and  bubbles  of  oxygen  rise  freely.  Cool, 
by  placing  the  flask  under  running  water,  and  complete  the 
determination  by  either  of  the  following  procedures: 

(a)  Colorimetric. — Compare  the  color  of  the  solution  with  that 
of  a  standard  steel  similarly  treated. 

(6)  Titration. — Titrate  with  standard  sodium  arsenite  solution 
to  the  disappearance  of  the  pink  color.  (See  Bismuthate  method.) 

6.  GRAVIMETRIC  DETERMINATION  OF  MANGANESE 

This  method  is  given  last  because  it  involves  more  manipula- 
tion than  any  of  the  preceding  methods  and,  for  this  reason 
alone,  is  not  suitable  for  a  busy  laboratory  although  it  may  well 
serve  as  a  reliable  method  for  use  in  judging  the  accuracy  of 
other  methods. 


MANGANESE 


71 


Principle. — One  of  the  best  methods  for  separating  manganese 
from  iron  in  the  analysis  of  cast  iron,  steel  and  other  alloys  low 
in  manganese,  is  the  Rothe  ether  separation  which  is  based  upon 
the  fact  that  ferric  chloride  is  very  soluble  in  ether  whereas 
manganese  chloride  is  not. 

If  two  non-miscible  solvents  are  in  contact  with  one  another 
and  a  third  substance  is  present  which  is  soluble  in  both  liquids, 
the  ratio  of  the  concentrations  (quantities  present 
in  a  unit  of  volume  of  each  solvent)  of  this  sub- 
stance in  the  two  solvents  after  equilibrium  has 
been  established  will  be  constant  at  any  given 
temperature  provided  the  solute  has  the  same 
molecular  weight  in  both  solutions.  This  is  the 

so-called     distribution     law.     The    ratio    —  =  fc, 

where  c\  represents  the  concentration  in  one 
solution  and  c%  the  concentration  in  the  other, 
is  called  the  distribution  coefficient. 

After  removing  the  ferric  chloride  by  shaking 
the  hydrochloric  acid  solution  with  ether,  it  is 
then  a  question  of  separating  the  manganese 
from  other  metals  and  acids  that  are  not  dis- 
solved by  the  ether  but  remain  in  the  aqueous 
acid  solution. 

Requisite  Apparatus  and  Solutions. — For  sep- 
arating   ferric    chloride    from    the   chlorides   of 
manganese,  nickel,  aluminium,  etc.,  the  Rothe 
shaking   funnel   shown   in   Fig.   13  is  suitable.1 
To  accomplish  a  satisfactory  separation  of  the  iron  from  the  man- 
ganese it  is  desirable  to  have  on  hand  1  or  2  liters  of  the  following 
solutions : 

1.  Hydrochloric  Acid  (d.  1.10). 

2.  Ether-hydrochloric  Acid,   A. — Hydrochloric   acid    (d.    1.19) 
saturated  with  ether.     To  prepare  this  reagent,  ether  is  added 
gradually,   in   small   portions,   to    hydrochloric   acid    (d.    1.19), 

1  The  apparatus  can  be  purchased  in  two  sizes;  with  each  funnel  hold- 
ing about  110  c.c.,  suitable  for  the  analysis  of  5  g.  of  steel  or  less,  and 
with  each  funnel  holding  about  250  c.c.,  suitable  for  the  analysis  of  15  g. 
of  steel. 


FIG.  13. 


72  CHEMICAL  ANALYSIS  OF  METALS 

until  a  layer  of  ether  is  formed  on  top  of  the  acid.  Considerable 
heat  is  evolved  as  the  ether  dissolves  in  the  acid,  so  that  it  is  advis- 
able to  cool  the  solution  from  time  to  time  by  allowing  cold  water 
to  run  over  the  bottle  while  it  is  being  shaken.  One  hundred 
cubic  centimeters  of  hydrochloric  acid  (d.  1.19)  will  dissolve 
about  150  c.c.  of  ether. 

3.  Ether-hydrochloric  Acid,  B. — This  is  prepared  in  the  same 
way  with  ether  and  hydrochloric  acid  (d.  1.10).  One  hundred 
cubic  centimeters  of  hydrochloric  acid  (d.  1.10)  will  dissolve  about 
30  c.c.  of  ether. 

In  separating  the  manganese  from  the  other  metals  that  are 
left  in  the  hydrochloric  acid  solution,  a  spacious  platinum  dish, 
11  to  13  cm.  in  diameter,  is  required  and  should  have  handles 
soldered  to  opposite  parts  of  the  upper  edges.  For  holding  the 
dish,  Rothe  recommends  using  small  clamps  as  shown  in  Fig.  14. 


FIG.  14. 

Procedure. — Weigh  out  10  g.  of  material  containing  up  to  1 
per  cent  manganese,  or  5  g.  if  the  manganese  content  is  higher, 
into  a  porcelain  dish  of  14  or  15  cm.  diameter,  cover  the  dish 
with  a  watch-glass,  and  dissolve  the  sample  by  the  gradual 
addition  of  dilute  nitric  acid  (d.  1.18).  Continue  the  treat- 
ment exactly  as  described  for  the  determination  of  Silicon  by 
Method  IB.1 

1  Instead  of  using  the  filtrate  from  the  silicon  determination  by  Method 
15,  that  from  Method  \A  may  be  taken.  In  this  case  it  is  necessary  to  make 
sure  that  all  the  iron  is  converted  into  ferric  chloride.  To  this  end,  concen- 
trate the  nitrate  from  the  silicon  determination  in  a  porcelain  dish  until  a 
crust  (ferrous  chloride)  begins  to  form  on  the  edges  of  the  solution.  Then 
cover  the  dish  with  a  watch-glass  and  add  dilute  nitric  acid  (d.  1.18)  to 
the  hot  hydrochloric  acid  solution  as  long  as  the  latter  is  colored  dark  brown 
and  nitric  oxide  is  evolved.  When  the  oxidation  of  the  iron  is  complete, 
wash  off  the  cover  glass  and  evaporate  with  hydrochloric  acid  (d.  1.10) 
to  expel  the  excess  nitric  acid.  The  concentrated  solution  is  then  ready  for 
the  ether  separation. 


MANGANESE  73 

If,  after  volatilizing  the  silica  by  treatment  with  sulfuric  and 
hydrofluoric  acids,  a  dark-colored  residue  is  obtained,  this  must 
be  treated  by  itself  for  manganese,  fusing  with  sodium  hydroxide 
and  sodium  peroxide  as  described  on  p.  76. 

Evaporate  the  filtrate  from  the  silicon  determination  in  a 
procelain  dish  until  it  becomes  very  viscous  but  without  the 
separation  of  any  crystals.  The  solution  is  then  ready  for  the 
ether  separation.  Pour  the  concentrated  ferric  chloride  solu- 
tion into  the  upper  bulb  of  the  shaking  funnel  (Fig.  13)  and 
rinse  out  the  dish  several  times  with  a  little  hydrochloric  acid 
(d.  1.10)  using  only  1  or  2  c.c.  of  the  acid  for  each  rinsing; 
when  the  last  portion  of  acid  added  to  the  dish  is  not  colored 
yellow  by  ferric  chloride,  the  washing  is  complete.  It  is  impor- 
tant at  this  point  to  avoid  the  use  of  too  much  hydrochloric  acid 
because  the  ether  separation  is  most  successful  when  the  volume 
of  the  hydrochloric  acid  solution  is  kept  as  small  as  possible. 
With  a  little  care  it  is  possible  to  wash  out  the  dish  thoroughly 
without  using  more  than  10  or  15  c.c.  of  the  acid.  When  all  the 
ferric  chloride  solution  has  been  transferred  to  the  upper  bulb 
of  the  shaking  funnel,  shake  the  solution,  and,  as  considerable 
heat  is  evolved,  cool  to  below  15°  by  holding  the  bulb  under  a 
stream  of  running  water.  If  the  solution  is  warm  when  the 
ether  is  introduced,  some  of  the  ferric  chloride  is  reduced  by  the 
ether  and  the  resulting  ferrous  chloride  is  left  with  the  manga- 
nese chloride  in  the  hydrochloric  acid  solution. 

According  to  Rothe's  directions  for  removing  ferric  chloride  by 
ether  from  a  solution  in  aqueous  hydrochloric  acid,  it  is  next 
necessary  to  add  ether-hydrochloric  acid  solution  A  until  6  c.c. 
of  the  latter  are  present  for  each  gram  of  dissolved  iron.  Shake 
the  solution  and  cool.  This  addition  of  the  ether-hydrochloric 
acid  serves  partly  to  give  the  proper  hydrochloric  acid  concen- 
tration for  a  successful  separation  by  ether  and  it  also  serves 
to  prevent,  as  far  as  possible,  the  evolution  of  heat  which  takes 
place  when  ether  is  added  to  a  hydrochloric  acid  solution  of 
ferric  chloride. 

Next,  add  ether  until  the  upper  bulb  is  nearly  full,  close  the 
stopcock  and  shake.  If  the  upper  bulb  becomes  at  all  warm, 
cool  under  running  water. 

Fasten  the  shaking  funnel,  at  the  narrow  part  above  the  upper 


74  CHEMICAL  ANALYSIS  OF  METALS 

bulb,  in  a  clamp  attached  to  a  ring  stand  and  allow  the  liquid  to 
remain  quiet  for  some  time.  In  this  way,  two  layers  are  obtained. 
The  upper  layer  is  green  and  consists  chiefly  of  ferric  chloride 
dissolved  in  ether.  The  lower  layer  consists  of  a  hydrochloric 
acid  solution  containing  the  chlorides  of  most  of  the  other  con- 
stituents of  the  material  which  is  being  analyzed.  Some  hydro- 
chloric acid  is  present  in  the  ether  solution  and  some  ether  is 
present  in  the  lower  layer.  The  color  of  the  latter  depends  upon 
what  metals  other  than  iron  are  present  in  the  original  substance. 

When  chromium,  nickel  or  much  vanadium  is  present,  the  color 
of  the  aqueous  hydrochloric  acid  solution  is  green  or  bluish-green; 
if  these  elements  are  absent  the  solution  is  usually  yellow  owing 
to  the  presence  of  small  quantities  of  ferric  chloride.  Often,  a 
brownish-yellow  solution  is  obtained  when  titanium  is  present; 
with  considerable  titanium  and  insufficient  acid  it  sometimes  hap- 
pens that  flakes  of  titanium  dioxide  are  deposited  (see  Titanium). 

By  opening  both  the  upper  and  middle  stopcocks,  allow  the 
hydrochloric  acid  solution  to  run  into  the  lower  bulb  but  take 
care  to  close  the  middle  stopcock  as  soon  as  the  line  of  demarca- 
tion between  the  two  layers  of  liquid  is  reached;  none  of  the 
upper  ethereal  solution  should  pass  into  the  middle  lower  bulb 
at  this  time,  or  into  the  boring  of  the  middle  stopcock.  Allow 
the  solution  in  the  upper  bulb  to  stand  a  little  longer  and  again 
drain  off  the  hydrochloric  acid.  To  wash  out  the  boring  of 
the  middle  stopcock,  add  a  few  cubic  centimeters  of  ether-hydro- 
chloric acid  solution  B,  and,  without  shaking,  drain  off  into  the 
lower  bulb  the  acid  that  collects  below  the  ether.  The  upper 
bulb  now  contains  an  olive  green  solution  chiefly  of  ferric  chloride 
and  hydrochloric  acid  in  ether,  and  the  lower  bulb  contains  an 
aqueous  hydrochloric  acid  solution  of  the  chlorides  of  manganese, 
nickel,  cobalt,  etc.  To  remove  small  quantities  of  these  last  ele- 
ments that  remain  adhering  to  the  ether  solution  in  the  upper 
bulb,  add  10  c.c.  of  ether-hydrochloric  acid  solution  B,  and  to 
remove  small  quantities  of  ferric  chloride  that  are  present  in  the 
solution  contained  in  the  lower  bulb,  nearly  fill  it  with  ether. 
Close  both  stopcocks  and  shake  well.  After  the  layers  have 
formed  again,  the  lower  layer  in  the  upper  bulb  contains  some 
more  of  the  manganese,  etc.,  together  with  a  little  ferric  chloride 
that  has  been  shaken  out  of  the  ether.  In  the  lower  bulb,  how- 


MANGANESE  75 

ever,  the  bottom  layer  ought  not  to  contain  more  than  1  or  2  mg. 
of  iron.  It  is  the  purpose  of  subsequent  treatment  to  remove  all 
the  metal  chlorides  except  ferric  chloride  from  the  ether  layer  in 
the  upper  bulb  and  to  free  these  hydrochloric  acid  extracts  from 
iron  as  far  as  possible  by  shaking  in  the  lower  bulb  with  ether 
containing  very  little  ferric  chloride. 

Allow  the  hydrochloric  acid  solution  in  the  lower  bulb  to  run 
into  the  porcelain  dish  that  was  used  previously  in  the  analysis, 
and  rinse  out  the  boring  of  the  stopcock  and  the  tubing  below  it 
with  a  few  cubic  centimeters  of  ether-hydrochloric  acid  solution 
B.  Then  allow  the  lower  layer  in  the  upper  bulb  to  flow  into 
the  lower  bulb  and  likewise  rinse  the  upper  bulb  with  a  little 
ether-hydrochloric  acid.  To  remove  more  of  the  metal  chlorides 
from  the  ether  in  the  upper  bulb,  again  add  10  c.c.  of  ether- 
hydrochloric  acid  solution  B,  shake  and  remove  the  bottom 
layers  in  each  bulb  by  the  same  operations  as  before.  After  the 
two  layers  have  separated  in  each  bulb,  add  the  lower  layer  in  the 
bottom  bulb  to  the  contents  of  the  porcelain  dish  and  allow  the 
lower  layer  in  the  upper  bulb  to  drain  into  the  lower  bulb.  To  be 
on  the  safe  side,  repeat  this  treatment  with  10  c.c.  of  ether- 
hydrochloric  acid  solution  B  a  third  and  fourth  time.  Then,  as 
a  rule,  the  separation  is  as  complete  as  is  necessary  and  it  may 
be  assumed  that  the  solution  in  the  porcelain  dish  now  contains 
all  the  manganese,  nickel,  cobalt,  chromium,  aluminium,  copper, 
titanium,  sulfuric  acid,  phosphoric  acid,  and  vanadium  together 
with  small  quantities  of  iron. 

Large  amounts  of  alkali  salts  cause  trouble;  the  ether  causes 
them  to  precipitate  and  the  deposited  salts  tend  to  clog  the  bor- 
ings in  the  stopcocks.  For  this  reason  the  use  of  alkali  salts 
must  be  avoided  in  preparing  a  solution  for  treatment  with 
ether.  Thus  oxidation  must  be  accomplished  with  nitric  acid 
rather  than  with  potassium  chlorate  and  any  excess  of  acid 
removed  by  volatilization  rather  than  by  neutralization  with 
ammonia. 

In  the  apparatus,  the  iron  is  left  as  ferric  chloride  dissolved  in 
ether  and  hydrochloric  acid.  By  shaking  with  water,  the  greater 
part  of  the  ether  can  be  separated  from  the  ferric  chloride  and 
the  solution  of  the  latter  may  be  used  for  the  determination  of 
iron  (see  Iron) .  When  the  method  is  used  frequently,  it  is  well 


76  CHEMICAL  ANALYSIS  OF  METALS 

to  recover  the  ether.  After  washing  it  with  sodium  hydroxide 
solution,  and  drying  over  calcium  chloride,  it  can  be  easily 
distilled  from  a  steam  bath.  It  is  necessary  to  keep  all  gas 
flames  away  from  the  vicinity  of  the  distilling  apparatus  on 
account  of  the  danger  of  the  vapors  taking  fire. 

Drive  off  the  ether  from  the  hydrochloric  acid  extract  contain- 
ing the  manganese  and  other  metals  by  heating  the  porcelain 
dish  at  one  of  the  cooler  places  on  the  steam  bath  and  then 
evaporate  to  dryness.  Take  up  the  residue  in  a  little  dilute 
hydrochloric  acid,  rinse  the  solution  into  a  100-c.c.  beaker  and 
precipitate  any  copper  present  by  the  addition  of  a  few  cubic 
centimeters  of  saturated  hydrogen  sulfide  water,  stirring  with 
a  glass  rod  until  the  copper  sulfide  precipitate  collects  together 
and  settles.  Then  filter  into  the  original  porcelain  dish,  add 
a  little  sulfuric  acid  to  the  filtrate  and  evaporate  to  dryness. 
Dissolve  the  residue  in  a  little  dilute  sulfuric  acid  and  transfer 
the  solution  to  a  platinum  dish  of  11  to  13  cm.  diameter  (Fig. 
14).  The  quantity  of  sulfuric  acid  used  must  be  adjusted  so 
that  in  the  following  evaporation  all  the  chlorides  present  will  be 
changed  to  sulfates  and  upon  stronger  ignition  (on  the  Finkener 
tower)  a  slight  excess  will  be  evolved  in  fumes.  After  this  treat- 
ment is  accomplished,  allow  the  dish  to  cool.  It  is  now  ready 
for  the  fusion. 

Fusion  with  caustic  soda  serves  to  free  the  manganese  (to- 
gether with  any  nickel,  cobalt  and  iron),  from  phosphoric  acid, 
chromium,  vanadium  and  aluminium. 

According  to  the  amount  of  sulfates  present,  dissolve  from  2  to 
5  g.  of  pure  sodium  hydroxide  in  a  platinum  crucible  with  as 
little  water  as  possible,  and  add  the  solution  to  the  contents  of 
the  platinum  dish.  The  metal  salts  are  at  once  decomposed  by 
the  alkali.  Take  hold  of  the  dish  in  some  such  way  as  shown  in 
Fig.  14,  and  carefully  evaporate  the  solution  to  dryness  by  mov- 
ing the  dish  back  and  forth  over  a  small  Bunsen  flame.  Too 
rapid  evaporation  will  cause  loss  by  spattering.  Continue  the 
heating  till  the  solid  melts  but  avoid  overheating.  When  a 
quiet  fusion  is  obtained,  allow  the  mass  to  cool  somewhat  and 
sprinkle  over  the  top  a  little  potassium  chlorate  or  sodium  per- 
oxide (a  quantity  such  as  can  be  held  on  the  point  of  a  penknife 
suffices).  Turn  up  the  Bunsen  flame  just  a  little  and  heat  the 


MANGANESE  77 

dish,  while  moving  it  about,  until  the  entire  contents  are  fused 
and  no  lumps  of  undecomposed  sodium  peroxide  are  visible. 

Heating  any  part  of  the  dish  more  strongly  than  is  necessary 
to  accomplish  fusion  must  be  avoided,  as  otherwise  the  platinum 
dish  will  be  attacked.  If  care  is  exercised,  however,  this  opera- 
tion can  be  carried  out  with  either  potassium  chlorate  or  sodium 
peroxide  without  the  platinum  dish  being  injured. 

After  cooling  the  fusion,  remove  the  holders,  cover  the  dish 
with  a  watch-glass  and  dissolve  the  contents  by  adding  about 
60  c.c.  of  hot  water;  any  excess  of  sodium  peroxide  is  decomposed 
by  this  treatment  and  oxygen  is  evolved.  Treat  the  solution, 
which  is  usually  colored  green  by  manganate,  with  a  little  more 
sodium  peroxide;  this  decomposes  the  manganate,  forming  man- 
ganese dioxide  with  evolution  of  oxygen. 

To  destroy  the  excess  of  sodium  peroxide,  heat  the  covered  dish 
and  its  contents  for  half  an  hour  on  the  steam  bath.  Then  rinse 
into  a  300  to  400-c.c.  beaker,  dilute  with  water  to  about  200  c.c. 
and  allow  the  precipitate  to  settle.  Usually  a  slight  yellowish- 
brown  stain  remains  in  the  platinum  dish.  Dissolve  this  with 
a  little  dilute  sulfuric  acid  and  a  small  crystal  of  oxalic  acid 
but  do  not  add  this  solution  to  the  main  solution  at  present. 

In  the  analysis  of  most  iron  and  steel  samples,  the  solution 
above  the  manganese  dioxide  precipitate  (which  also  contains 
nickel,  cobalt  and  iron)  is  usually  colored  more  or  less  yellow  by 
a  little  chromium.  Allow  the  solution  to  cool,  and,  without 
stirring  up  the  precipitate,  decant  the  clear,  supernatant  liquid 
through  7  or  9  cm.  filter,  according  to  the  size  of  the  precipitate. 
Add  hot  water  to  the  precipitate,  allow  it  to  settle  and  again 
decant.  Repeat  this  operation  once  or  twice  more,  and  place  a 
fresh  beaker,  or  Erlenmeyer  flask,  under  the  funnel.  Then,  if 
subsequent  washings  run  through  the  filter  turbid,  it  will  not 
be  necessary  to  refilter  the  entire  solution.  Transfer  the  pre- 
cipitate to  the  filter  and  wash  it  carefully.  When  the  alkali 
salts  are  all  removed  there  is  danger  of  some  of  the  precipitate 
becoming  colloidal  and  passing  through  the  filter.  This  may 
be  avoided,  if  toward  the  end  of  the  washing  a  dilute  solution 
of  ammonium  sulfate  is  used  instead  of  pure  water,  or  if  from 
time  to  time  a  small  crystal  of  ammonium  sulfate  is  placed 
in  the  filter  and  the  washing  done  with  pure  water. 


78  CHEMICAL  ANALYSIS  OF  METALS 

The  combined  nitrate  contains  all  the  chromium  and  alu- 
minium besides  the  phosphorus  and  vanadium.  It  can  be  used 
for  the  determination  of  these  elements. 

Upon  the  filter  are  the  hydrated  oxides  of  manganese,  nickel 
and  cobalt  together  with  a  little  iron  that  remained  in  the 
aqueous  solution  after  treatment  with  ether.  Dissolve  the 
precipitate  in  a  little  concentrated  hydrochloric  acid.  If  there 
is  much  precipitate,  wash  as  much  as  possible  into  a  small  beaker, 
place  the  beaker  under  the  funnel  and  dissolve  the  precipitate 
by  pouring  strong  hydrochloric  acid  through  the  filter;  if  there 
is  only  a  little  precipitate,  place  the  beaker  at  once  under  the 
funnel  and  dissolve  all  the  precipitate  on  the  filter.  Wash 
the  filter  thoroughly  with  hot,  dilute  hydrochloric  acid.  Add 
to  the  solution  the  sulfuric  and  oxalic  acid  solution  that  was 
previously  obtained  by  dissolving  the  stain  on  the  platinum 
dish.  Evaporate  on  the  steam  bath  to  remove  free  chlorine  and 
until  the  volume  of  liquid  is  small;  the  color  of  the  solution  may 
be  yellow  from  a  little  dissolved  ferric  chloride,  or  more  or 
less  yellowish  green  if  nickel  is  present. 

When  much  nickel  is  present,  the  treatment  of  the  solution, 
after  the  removal  of  the  greater  part  of  the  iron  by  shaking  with 
ether,  should  be  carried  out  as  described  on  page  85. 

To  remove,  now,  small  quantities  of  iron  that  escaped 
solution  in  ether  (when  the  operation  was  properly  carried  out 
this  should  amount  to  only  a  few  milligrams)  nearly  neutralize 
the  free  acid  by  the  addition  of  ammonia  but  do  not  continue 
adding  ammonia  until  a  permanent  precipitate  is  formed.  To 
the  barely  acid  solution,  add  1  or  2  c.c.  of  20  per  cent  ammonium 
acetate  solution  and  heat  just  to  boiling.  Filter  off  the  reddish- 
brown  flocks  of  basic  ferric  acetate  through  a  small  filter  and 
wash  well  with  hot  water.  If  the  •  precipitate  is  at  all  bulky, 
dissolve  it  in  hydrochloric  acid  and  repeat  the  basic  acetate 
separation  exactly  as  before. 

Combine  the  filtrates  from  the  basic  acetate  precipitation, 
make  slightly  acid  with  acetic  acid  and  saturate  the  cold  solution 
with  hydrogen  sulfide  gas.  Without  interrupting  the  current  of 
hydrogen  sulfide,  slowly  heat  the  solution  to  boiling,  then  turn 
out  the  flame  and  allow  the  solution  to  cool  while  hydrogen 
sulfide  is  constantly  passing  through  it.  After  the  precipitated 


MANGANESE  79 

nickel  and  cobalt  sulfides  have  settled,  filter  and  wash  carefully 
with  water.  Concentrate  the  filtrate  in  a  porcelain  dish;  often 
during  this  evaporation  some  more  nickel  sulfide  precipitates 
out.  Transfer  the  solution  to  a  beaker  and  once  more  introduce 
hydrogen  sulfide.  After  filtering  off  any  nickel  sulfide  that  may 
have  formed,  evaporate  to  expel  hydrogen  sulfide. 

Transfer  the  solution  containing  the  manganese  to  a  400-c.c. 
beaker,  dilute  to  about  200  c.c.  and  neutralize  with  ammonia. 
Add  a  little  bromine  water  and  a  slight  excess  of  ammonia.  Heat 
the  liquid  and  stir  to  facilitate  the  formation  of  the  manganese 
dioxide  precipitate.  By  adding  more  bromine  and  making 
slightly  ammoniacal  again,  make  sure  that  the  precipitation  of 
the  manganese  was  complete.  In  case  an  appreciable  quantity 
of  precipitate  was  formed  the  last  time,  repeat  the  operation. 

After  allowing  to  stand  a  short  time  on  the  water  bath,  filter 
the  liquid  through  an  ashless  paper  and  wash  the  precipitate  a 
few  times  with  hot  water.  Test'  the  filtrate  for  manganese  by 
treatment  with  bromine  and  ammonia  and,  in  case  no  pre- 
cipitate forms,  evaporate  the  liquid  to  dryness,  which  sometimes 
causes  the  deposition  of  small  quantities  of  manganese  dioxide.1 

It  is  a  quite  common  practice  among  chemists  to  ignite  and 
weigh  this  precipitate,  calling  it  Mn3O4.  According  to  the  quan- 
tity of  precipitate  and  the  ignition  temperature,  however,  the 

1  In  a  dilute  acid  solution  bromine  has  scarcely  any  oxidizing  effect  upon 
manganous  ions.  In  other  words  the  reaction: 

Mn++  +  Br2  +  2H2O±-+MnO2  +  2Br+  +  4H+ 

reaches  an  equilibrium  before  little,  if  any,  of  the  manganese  is  precipitated. 
On  the  other  hand,  when  the  acid  is  neutralized  the  equilibrium  of  the  above 
reaction  is  disturbed  and  the  precipitation  of  the  manganese  as  dioxide  may 
be  made  quantitative.  Ammonia  is  used  in  the  above  test  as  a  neutralizing 
agent.  Bromine,  however,  also  reacts  directly  with  ammonia  and  oxidizes  a 
part  of  its  nitrogen  to  free  nitrogen  in  the  sense  of  the  following  equation : 

8NH3  +  3Br2  =  6NH4Br  +  N2 

This  reaction  often  goes  a  little  farther  and  part  of  the  ammonium  salt  is 
oxidized,  leaving  the  solution  slightly  acid; 

2NH4+  +  3Br2±+N2  +  6Br~  +  8H+ 

Although  this  last  reaction  takes  place  only  to  a  slight  extent,  it  is  clear  that, 
as  a  result  of  the  two  last  reactions,  the  precipitation  of  the  manganese  is 
made  more  difficult.  This  is  the  reason  for  the  repeated  treatment  with 
bromine  and  ammonia. 


80  CHEMICAL  ANALYSIS  OF  METALS 

oxygen  content  varies  somewhat  so  that  it  is  better  to  convert 
it  into  either  pyrophosphate  or  sulfate.  In  either  of  the  latter 
forms,  the  composition  of  the  ignited  precipitate  is  constant 
and  the  results  obtained  are  exact. 

To  convert  the  manganese  dioxide  precipitate  into  pyro- 
phosphate, dissolve  it  in  hot,  dilute  hydrochloric  acid  to  which 
a  few  cubic  centimeters  of  sulfurous  acid  have  been  added.  Pour 
the  acid  through  the  filter  and  wash  the  latter  thoroughly  with 
hot  water.  Dilute  the  solution  to  100  c.c.,  add  20  g.  of  ammon- 
ium chloride,  5  to  10  c.c.  of  a  cold,  saturated  solution  of  disodium 
phosphate  and  ammonia,  drop  by  drop,  until  a  slight  excess  is 
present.  Heat  to  boiling  and  keep  at  this  temperature  for  3  or  4 
min.,  or  until  the  precipitate  assumes  a  silky  crystalline  appear- 
ance. Allow  the  solution  to  cool. 

When  a  precipitate  can  be  dried  easily  and  completely  at  a 
temperature  not  far  from  the  boiling  point  of  water,  it  used 
to  be  common  practice  to  filter  it  upon  a  weighed  (tared)  filter. 
Gooch,  however,  proposed  the  use  of  a  perforated  crucible  con- 
taining a  felt  of  asbestos  fibers  to  serve  as  filtering  medium. 
This  has  two  advantages:  first,  the  crucible  may  be  dried  at  a 
temperature  much  higher  than  could  be  used  with  a  paper  filter; 
second,  suction  can  be  used  during  filtration  and  considerable 
time  saved.  If  the  asbestos  felt  is  properly  prepared  and  the 
crucible  is  .dried  originally  to  constant  weight  at  the  temperature 
to  which  the  precipitate  is  to  be  heated,  the  results  are  as  good 
as  those  obtained  by  any  other  method. 

To  prepare  the  asbestos  felt,  first  digest  the  asbestos  fibers, 
in  pieces  about  0.5  cm.  long,  for  about  an  hour  on  the  water  bath 
with  strong  hydrochloric  acid.  Collect  the  asbestos  upon  a 
filter  plate  and  wash  out  all  the  acid  with  water.  Shake  it  up 
in  a  bottle  with  water  so  that  a  thin  suspension  is  formed. 
Stretch  a  piece  of  "bill-tie"  rubber  tubing  over  a  funnel,  Fig.  15, 
and  place  the  crucible,  T,  in  the  opening.1  The  funnel  should 
1  Instead  of  using  the  flat  rubber  band  to  support  the  crucible,  L.  H.  Bailey 
has  devised  a  Gooch  crucible  holder  which  is  shown  in  Fig.  16.  It  is  made 
of  rubber  and  fits  an  ordinary  2-in.  glass  funnel.  The  funnel  is  inserted  in 
a  perforated  rubber  stopper  which  in  turn  fits  the  suction  flask.  The  upper 
edge  of  the  holder  projects  over  the  upper  edge  of  the  funnel  and  the  lower 
edge  of  the  holder  rests  on  the  side  of  the  funnel.  When  suction  is  applied 
the  holder  fits  tightly  to  the  funnel. 


MANGANESE 


81 


be  large  enough  so  that  the  crucible  is  suspended  by  the  rubber 
without  touching  the  sides  of  the  funnel.  Pour  enough 
of  the  asbestos  suspension  into  the  crucible,  applying  gentle 
suction,  to  produce  a  layer  1  or  2  mm.  thick.  Place  a  small 
filter  plate  upon  this  layer  and  pour  a  little  more  asbestos  into 
the  crucible.  Pour  water  through  the  crucible  until  no  more 
asbestos  fibers  are  washed  away.  To  see  the  fibers,  pour  the 
liquid  into  a  small  beaker  and  hold  it  up  to  the  light. 


FIG.  15. 


FIG.  16. — Sectional  view  of 
Bailey's  Gooch  crucible  holder 
with  funnel  and  crucible. 


Instead  of  using  an  asbestos  felt,  Munroe,1  Neubauer  and 
others  have  recommended  the  use  of  platinum  sponge.  To  pre- 
pare such  a  felt,  place  the  perforated  crucible  upon  several  layers 
of  filter  paper  and  pour  into  it  a  mixture  of  ammonium  chloro- 
platinate  crystals  ground  up  with  a  little  alcohol.  Heat  the 
crucible  carefully  and  shape  the  felt  to  the  bottom  of  the  cru- 
cible, finally  burnishing  it  slightly  with  the  aid  of  a  glass  rod  of 
suitable  shape. 

The  manganese  ammonium  phosphate  precipitate  may  be 
filtered  off  through  a  washed  filter,  ignited  carefully  in  a 

1  MUNROE,  C.  E.,  J.  anal.  Chem.,  2,  241;  Chem.  News,  58,  101;  SNELLING, 
W.  O.,  J.  Am.  Chem.  Soc.,  31,  456  and  SWETT,  O.  D.,  Ibid.,  31,  928.    The  last 
reference  gives  a  table  of  suitable  solvents  for  removing  ignited  precipitates. 
6 


82  CHEMICAL  ANALYSIS  OF  METALS 

porcelain  crucible  and  weighed  as  manganese  pyrophosphate. 
It  is  fully  as  satisfactory,  however,  to  use  either  the  Gooch  or 
Munroe  crucible.  First,  dry  the  crucible  ^  hr.  at  about  130° 
and  then  ignite  it  in  an  electric  furnace,  or  within  a  larger  crucible 
heated  by  a  gas  flame.  In  this  way  there  is  no  danger  of  gases 
from  the  flame  coming  in  contact  with  the  asbestos  or  platinum 
felt.  After  igniting  at  a  high  temperature  for  about  10  min., 
allow  the  crucible  to  cool  in  the  air  somewhat1  and  then  let  it 
remain  half  an  hour  in  a  desiccator  before  weighing. 

Filter  off  the  manganese  ammonium  phosphate  using  either 
the  weighed  Munroe  or  Gooch  crucible,  and  wash  the  precipitate 
thoroughly  with  a  cold,  10  per  cent,  solution  of  ammonium  nitrate. 
Dry  the  crucible  and  its  contents  for  at  least  %  hr.  at  about  130° 
and  then  gradually  raise  the  temperature  until  finally  a  high 
heat  is  obtained.  Duringt  his  last  heating  the  manganese  am- 
monium phosphate  is  changed  to  manganese  pyrophosphate: 

2MnNH4PO4  =  Mn2P2O7  +  2NH3  +  H2O 

It  is  very  important  not  to  ignite  the  precipitate  too  quickly, 
as  in  that  case  the  ammonia  acts  upon  the  phosphate,  reducing 
it  and  turning  it  black;  it  is  a  tedious  operation  to  whiten  such 
a  precipitate  by  ignition. 

To  convert  the  manganese  dioxide  precipitate  into  sulfate, 
ignite  it  with  the  filter  in  a  weighed  porcelain  crucible,  cover  the 
crucible  with  a  watch-glass,  and  dissolve  the  precipitate  in 
hydrochloric  acid  (d.  1.12).  Heat  carefully  until  the  chlorine 
is  expelled  and  add,  for  each  0.1  g.  of  precipitate,  about  0.5  c.c. 
of  dilute  sulfuric  acid  (1:5).  To  remove  the  excess  of  the  latter, 
heat  the  crucible  and  its  contents  in  an  air  bath,  which  may  be 
prepared  according  to  the  suggestion  of  Gooch  and  Austin,2 
with  the  aid  of  a  larger  porcelain  crucible.3  The  outer  crucible 

1  If  the  very  hot  crucible  is  placed  immediately  in  a  desiccator  with  a 
tightly  fitting  cover,  the  expansion  of  the  air  causes  the  top  of  the  desiccator 
to  jump  up  and  down  several  times  and  then,  on  cooling,  a  partial  vacuum 
is  produced  in  the  desiccator.     As  a  result  the  crucible  cools  very  slowly. 
If  weighed  while  still  warm,  it  will  weigh  too  little,  owing  to  air  currents 
rising  from  the  balance  pan.     Much  time  is  saved,  therefore,  by  allowing 
the  crucible  to  cool  somewhat  before  placing  it  in  the  desiccator. 

2  Z.  anorg.  Chem.,  17,  264  (1898). 

3  If  an  electrically-heated  drying  oven  is  available,  heat  the  crucible  in  it 
to  constant  weight  at  450  to  500°. 


MANGANESE  83 

(Fig.  17),  is  chosen  of  such  a  size  that  when  the  smaller  crucible 
is  placed  within  it,  and  suspended  by  a  piece  of  asbestos  cord 
wrapped  around  it,  or  by  means  of  a  small  triangle,  the  distance 
between  the  walls  of  the  two  crucibles  is  about  1  cm.  on  all  sides. 

Heat   the   outer   crucible   for  a  short  time    r—     , 

with  a  good  Bunsen  flame,  cool  and  weigh. 
Continue  the  heating  until  a  constant  weight 
is  obtained.  The  manganese  sulfate  should  be 
pale  pink,  not  brown  at  the  bottom,  and  should 
be  perfectly  soluble  in  water.  FlG-  17- 

Computation. — If  pi  is  the  weight  of  manganese  pyro phosphate 
and  s  the  weight  of  substance  taken,  then 

2Mn  X  pi  X  100      38.70»i 
— ™ — T^r\  ^,    ~  =  ~         ~  =  Per  cent  Mn 
Mn2P2O7Xs  s 

If  7?2  is  the  weight  of  the  manganese  sulfate  and  s  the  weight  of 
substance  taken,  then 

Mn  X  p2  X  100      36.38p2 

— TVT  or\    vx —  =  ~         ~  =  Per  cent  Mn 
MnSO4  X  s  s 

The  method  can  be  modified  to  advantage  in  the  analysis  of 
special  materials: 

(a)  Alloys  Rich  in  Manganese. — (Ferro-manganese,  metallic 
manganese,  etc.,  which  contain  only  little  iron).  Dissolve  from 
2  to  4  g.  of  metal1  in  nitric  acid,  decompose  the  nitrates  and 
remove  the  silica2  as  described  previously.  Carefully  add  am- 
monia to  the  filtrate  from  the  silica  until  the  solution  is  neutral, 
add  ammonium  acetate,  and  carry  out  a  basic  acetate  separation 
(cf.  p.  78).  If  there  is  a  considerable  precipitate  of  basic  ferric 
acetate,  redissolve  it  and  repeat  the  precipitation.  Make  the 
entire  filtrate  slightly  acid  with  acetic  acid  and  precipitate  the  cop- 
per, nickel  and  cobalt  with  hydrogen  sulfide.  Transfer  the  fil- 
trate to  a  calibrated  250-c.c.  flask,  when  it  is  at  the  laboratory 
temperature,  make  up  to  the  mark  and  thoroughly  mix  by 
pouring  back  and  forth  several  times  into  a  dry  beaker.  By 

1  As  regards  the  necessity  for  getting  a  representative  sample,  see  Part  II 
of  this  book. 

2  In  the  dehydration  of  the  silicic  acid,  the  dish  should  not  be  overheated  or 
there  is  danger  of  losing  some  manganous  chloride  by  volatilization. 


84  CHEMICAL  ANALYSIS  OF  METALS 

means  of  a  50-c.c.  pipette,  take  an  aliquot  part  for  the  manganese 
determination. l 

The  determination  of  the  manganese  can  now  be  carried  out 
in  the  same  way  as  before.  In  some  cases,  however,  calcium  is 
likely  to  be  present  and  then  the  manganese  dioxide  precipitate 
will  contain  some  of  this  element.2  It  is  better,  then,  to  pre- 
cipitate the  maganese  as  sulfide  by  passing  hydrogen  sulfide  into 
the  slightly  ammoniacal  solution.  The  manganese  sulfide  is 
easily  converted  into  sulfate  (cf.  p.  48). 

(b)  Alloys  Rich  in  Nickel. — (Nickel  steel  with  high  nickel 
content,  chrome-nickel  steel,  etc.).  To  avoid  the  difficulties 
involved  in  precipitating  considerable  nickel  in  the  presence  of 

1  To  avoid  error  in  taking  the  aliquot  part,  it  is  necessary  to  make  sure  that 
the  pipette  and  calibrated  flask  are  properly  calibrated.     This  is  particularly 
necessary  because  several  temperatures  have  been  suggested  as  standards  for 
calibration  purposes  and,  moreover,  both  flasks  and  pipettes  are  calibrated  in 
two  ways — for  contents  and  for  delivery.     In  this  case,  the  flask  should  be 
calibrated  for  contents  and  the  pipette  for  delivery.     A  simple  way  to  test 
the  flask  is  to  take  some  water  that  is  at  the  room  temperature  and  add  the 
contents  of  the  50-c.c.  pipette  five  times  to  the  dry  flask.     In  using  the 
pipette,  allow  the  pipette  to  flow  freely  and  when  the  liquid  stops  flowing, 
touch  the  sides  of  the  flask,  or  the  surface  of  the  liquid,  with  the  point  of  the 
pipette  to  remove  another  drop,  and  then  take  away  the  pipette  (do  not 
blow  through  it).     Place  a  mark  on  the  neck  of  the  flask  where  the  bottom 
of  the  meniscus  comes.     It  is  best  to  dry  the  flask  again  and  repeat  the 
operation.     It  makes  no  difference  now,  whether  the  250-c.c.  flask  or  the 
pipette  has  been  correctly  calibrated  because  it  is  known  that  the  pipette 
will  deliver  exactly  one-fifth  of  the  solution  in  the  flask.     It  is  important, 
however,  to  make  sure  that  the  solution  has  the  same  temperature  when 
made  up  to  the  mark  that  it  has  when  the  aliquot  part  is  taken.     If  the  solu- 
tion is  warm  when  made  up  to  the  mark  and  cools  during  the  pouring  back 
and  forth  into  the  beaker,  then  the  results  will  come  out  too  high  and 
conversely. 

If  there  is  a  balance  in  the  laboratory  capable  of  weighing  1  kg.  and 
sensitive  to  a  centigram,  it  is  more  accurate  to  use  it  for  dividing  the  solu- 
tion. Weigh  the  perfectly  dry  flask,  together  with  its  ground  glass  stopper, 
and  then  weigh  it  again  with  the  solution  in  it,  without  taking  special 
pains  to  bring  it  exactly  to  any  specified  volume.  Thoroughly  mix  the 
solution  and  pour  a  part  of  it  into  another  weighed  flask.  Stopper  this 
flask  and  again  weigh  it.  From  the  ratio  between  the  two  weights  of  the 
solution  the  corresponding  fraction  of  the  weight  of  sample  taken  for 
analysis  can  be  computed. 

2  cf.  REIS,  Z.  angew.  Chem.,  1892,  672. 


MANGANESE  85 

manganese,  due  to  the  fact  that  the  solubility  products  of  nickel 
and  manganese  sulfides  lie  comparatively  near  together,  it  is 
better  to  remove  most  of  the  nickel,  after  shaking  out  the  ferric 
chloride  with  ether,  in  the  following  manner:  Evaporate  the 
hydrochloric  acid  solution  to  dryness,  taking  care  not  to  set  fire 
to  the  ether  it  contains,  take  up  the  residue  in  hydrochloric 
acid  and  neutralize  the  excess  of  acid  with  ammonia.  Add 
bromine,  make  slightly  ammoniacal  again  and  heat.  By  this 
treatment,  the  greater  part  of  the  nickel  remains  in  solution 
forming  a  blue  liquid,  and  the  manganese  together  with  the 
remainder  of  the  iron  and  some  nickel  is  contained  in  the  pre- 
cipitate. Filter  off  the  brown  precipitate  and  again  test  the 
filtrate  for  manganese  by  treatment  with  bromine  and  ammonia. 
Dissolve  the  precipitated  oxides  on  the  filter  by  treating  with 
hydrochloric  acid1  (d.  1.12),  add  a  little  sulfuric  acid,  and 
evaporate  the  solution  on  the  Finkener  tower  until  fumes  of 
sulfuric  acid  are  evolved.  Fuse  the  residue  with  sodium  hydrox- 
ide and  either  sodium  peroxide  or  potassium  chlorate  and  thus 
remove  the  remainder  of  the  iron  and  nickel  by  the  method 
described  on  p.  78.  Eventually  determine  the  manganese  as 
sulfate  or  pyrophosphate.2 

(c)  Materials  Insoluble  in  Acid. — (Ferro-chrome,  ferro-tungsten, 
silico-manganese,  etc.). 

Such  materials  can  be  attacked  by  the  ignition  method 
described  in  the  chapter  on  Silicon.  It  is  usually  advantageous 
to  use  the  sodium  carbonate  and  magnesia  mixture  in  the  pro- 
portions suggested  by  Rothe. 

Weigh  out  from  0.5  to  2  g.  of  substance,  according  to  the 
probable  manganese  content,  ignite  it  with  sodium  carbonate 
and  magnesia,  transfer  the  ignited  mass  to  an  agate  mortar, 
moisten  it  with  water  and  rub  it  up  with  the  pestle  to  as  thin  a 
paste  as  possible.  Rinse  into  a  beaker,  dilute  with  hot  water 
to  a  volume  of  about  200  c.c.  and  reduce  the  manganate  by  adding 
a  little  sodium  peroxide.  After  destroying  the  excess  of  peroxide 
by  boiling  the  liquid,  allow  the  precipitate  to  settle,  decant  off 

1  If  the  precipitate  remains  on  the  filter  very  long,  it  may  be  necessary  to 
add  a  little  sulfurous  acid  to  the  hydrochloric  acid. 

2  If  phosphorus  and  manganese  are  not  present  to  an  appreciable  extent, 
the  fusion  with  sodium  hydroxide  and  peroxide  may  be  omitted.     The  iron 
and  nickel  are  then  removed  in  the  usual  way. 


86  CHEMICAL  ANALYSIS  OF  METALS 

the  supernatant  liquid  through  a  filter  and  wash  several  times 
by  decantation,  taking  pains  to  keep  the  precipitate  off  the 
filter  as  far  as  possible. 

Finally,  dissolve  the  washed  precipitate  in  the  beaker  by  the 
addition  of  hydrochloric  acid  (d.  1.12),  add  to  the  solution  the 
filter  with  the  small  deposit  of  manganese  dioxide  upon  it,  and 
heat  to  expel  chlorine.  Filter  off  the  filter  paper  shreds  and  any 
unattacked  material  and  wash  the  filter  with  water  containing 
hydrochloric  acid.  If  some  unattacked  material  is  found  (this 
usually  collects  in  the  bottom  of  the  beaker  in  the  form  of  small 
black  particles,  having  a  gritty  feeling  when  pressed  upon  with 
a  glass  stirring-rod)  burn  the  filter  in  a  platinum  dish  and  fuse 
the  ash  with  sodium  carbonate.  Take  up  the  product  of  the 
fusion  with  water  and  add  sodium  peroxide  to  reduce  the  manga- 
nate,  if  any  is  shown  to  be  present  by  the  green  color  of  the  aque- 
ous extract.  Filter  off  the  precipitate  of  manganese  and  ferric 
oxides,  etc.,  add  the  filtrate  to  that  obtained  from  the  fusion  with 
sodium  carbonate  and  magnesia,  and  add  the  hydrochloric  acid 
solution  of  the  precipitate  to  the  main  hydrochloric  acid  solution. 

The  alkaline  solution  thus  obtained  may  be  used  for  the 
determination  of  phosphorus  or  chromium. 

Evaporate  the  hydrochloric  acid  solution  of  the  precipitate 
containing  the  manganese  to  dryness  in  a  porcelain  dish  and 
heat  for  some  time  to  135°  over  an  asbestos  plate.  After  cooling, 
take  up  in  hydrochloric  acid  and  remove  the  silica  as  described 
on  p.  64. 

Dilute  the  filtrate  from  the  silica  to  about  250  c.c.,  neutralize 
the  free  acid  by  the  addition  of  ammonia,  add  ammonium  acetate 
and  precipitate  the  iron  as  basic  ferric  acetate,  as  described  on 
p.  78.  Usually  it  is  advisable  to  carry  out  a  second  basic  acetate 
separation. 

Make  the  filtrate  distinctly  acid  with  acetic  acid  and  intro- 
duce hydrogen  sulfide  to  precipitate  any  nickel  present.  Filter 
off  the  nickel  sulfide,  catching  the  filtrate  in  a  300-c.c.  beaker, 
and  precipitate  the  manganese  by  the  addition  of  bromine  and 
ammonia  (cf.  p.  79).  The  precipitation  may  be  hastened  by 
vigorous  stirring. 

Filter  off  the  precipitate,  wash  it  well  with  water,  and  pre- 
serve the  filtrate  in  order  to  test  it  for  manganese.  Transfer, 


MANGANESE  87 

by  means  of  a  stream  from  the  wash  bottle,  as  much  as  possible 
of  the  precipitate  to  a  beaker,  place  the  beaker  under  the  funnel 
and  pour  hydrochloric  acid  (d.  1.12)  through  the  filter. 
Wash  the  filter  thoroughly  and  heat  the  acid  to  dissolve  the 
manganese  dioxide.  Concentrate  the  solution  until  the  volume 
is  very  small  and  precipitate  the  manganese  as  sulfide,  using 
freshly  prepared  ammonium  sulfide1  as  reagent. 

To  carry  out  the  precipitation,  take  50  to  100  c.c.  of  ammonium 
sulfide  solution  (according  to  the  quantity  of  manganese  present), 
and  heat  it  just  to  boiling  in  a  300  to  400-c.c.  beaker.  Heat  the 
manganese  solution,  which  must  be  as  nearly  neutral  as  possible, 
and  pour  it  into  the  hot  ammonium  sulfide  solution.  Rinse  out 
the  beaker  that  contained  the  manganese  solution  and  heat 
the  liquid  a  short  time  in  order  to  obtain  a  precipitate  of  green 
manganese  sulfide  that  will  filter  well. 

After  allowing  all  the  precipitate  to  settle,  pour  the  liquid 
through  a  filter  that  runs  well2  and  wash  the  precipitate  with 
hot  water  containing  a  little  ammonium  sulfide.  Evaporate  the 
filtrate  and  washings  and  recover  any  manganese  that  it  may 
contain  by  treatment  with  bromine  and  ammonia.  This  treat- 
ment with  bromine  and  ammonia  should  be  repeated  to  be  sure 
that  all  manganese  has  been  precipitated. 

Ignite  the  manganese  sulfide  precipitate  in  a  weighed  porcelain 
crucible,  dissolve  the  resulting  manganomanganic  oxide  in 
hydrochloric  acid  (d.  1.12)  and  convert  it  into  the  anhydrous 
sulfate  as  described  on  p.  82.  The  small  quantity  of  manganese 
dioxide  recovered  from  the  filtrates  may  be  ignited  separately 
and  weighed  as  Mn304. 

1  To  prepare  ammonium  sulfide  free  from  polysulfide,  saturate  ammonia 
water   (d.   0.96)    with  hydrogen   sulfide  and  then  add  an  equal  volume  of 
ammonia  water. 

2  If  the  precipitate  at  first  runs  through  the  filter,   continue  to  filter 
(provided  the  liquid  does  not  run  too  slowly  through  the  filter),  and  eventu- 
ally transfer   all  the   precipitate  to  the  paper.     As  soon   as  the   filtrate 
begins  to  run  through  clear,  change  the  vessel  under  the  funnel  and  pour 
the  turbid  filtrate  through  the  filter  again.     In  filtering  keep  the  filter  nearly 
filled  all  the  time  and  do  not  wait  for  all  the  liquid  to  run  through  during 
the  washing.     Otherwise,  the  manganese  sulfide  oxidizes  on  the  filter,  dis- 
solves in  the  wash  water,  and  a  precipitate  of  manganese  sulfide  is  formed 
again  in  the  filtrate  which  contains  ammonium  sulfide. 


88  CHEMICAL  ANALYSIS  OF  METALS 

Short  Gravimetric  Method. — The  time  required  for  determin- 
ing manganese  gravimetrically  may  be  shortened  considerably 
up  to  the  point  of  the  ether  separation,  by  using  a  round-bottomed 
flask  instead  of  porcelain  casserole  for  dissolving  the  sample. 
For  samples  weighing  from  5  to  10  g.,  a  flask  of  about  500-c.c. 
capacity  is  suitable,  or  a  300-c.c.  flask  for  a  3-g.  sample. 

Weigh  the  sample  directly  into  the  flask,  dissolve  it  by  the 
gradual  addition  of  the  necessary  quantity  of  nitric  acid  (d. 
1.18)  heat  over  a  small  flame  until  solution  is  complete,  and 
evaporate  over  a  free  flame  while  keeping  the  flask  in  constant 
motion.  Hold  the  flask  by  a  clamp  attached  to  the  neck. 

When  the  solution  has  evaporated  to  dryness,  heat  care- 
fully to  decompose  the  nitrates,  allow  to  cool,  dissolve  the 
oxides  in  the  necessary  quantity  of  concentrated  hydrochloric 
acid  (d.  1.2)  again  evaporate  to  dryness,  and  continue  the 
heating  until  the  color  of  the  residue  is  dark  brown  but  not 
necessarily  until  it  becomes  red.  Cool,  dissolve  in  concentrated 
hydrochloric  acid  and  heat  until  there  is  no  ferric  oxide  visible 
in  the  bottom  of  the  flask.  Dilute  and  filter  off  the  silica. 
Transfer  the  solution  to  the  flask  again  and  evaporate  until  it 
is  ready  for  treatment  with  ether. 

This  method  of  working  is  not  suitable  when  it  is  desired  to 
determine  the  silicon  because  it  is  difficult  to  remove  the  last 
traces  of  silica  from  the  flask. 

Test  Analyses. — To  test  the  method  described  for  the  separa- 
tion of  manganese  from  iron,  25  c.c.  of  a  manganous  chloride 
solution,  containing  0.0354  g.  of  manganese,  were  mixed  with 
pure  ferric  chloride  solution,  corresponding  to  about  3.5  g.  of 
iron,  and  the  manganese  determined.  The  average  of  three 
closely  agreeing  analyses  gave  0.0364  g.  of  manganese  when 
weighed  as  Mn304  and  0.0354  g.  of  manganese  when  weighed 
as  MnSO4. 

ACCURACY  OF  THE  RESULTS  AND  PERMISSIBLE  DEVIATION 

Besides  errors  in  weighing,  certain  other  unavoidable  errors 
arise  which  in  careful  work  should  not  be  large.  In  general,  if 
the  manganese  is  weighed  as  sulfate  or  as  pyrophosphate,  the 
weight  of  the  final  precipitate  should  be  accurate  within  1  mg. 
when  the  precipitate  weighs  50  mg.  or  less  and  within  2  mg.  with 


MANGANESE  89 

larger  quantities.  According  to  the  amount  of  material  taken 
for  analysis  (e.g.,  5  g.  when  less  than  2  per  cent  of  manganese 
is  present  and  1  g.  otherwise)  this  will  correspond  to  the  follow- 
ing permissible  deviations  in  duplicate  results: 

From  To                                Deviation 

0.0  per  cent  0.2  per  cent ±0.01  per  cent 

0.2  per  cent  1.0  per  cent ±  0.02  per  cent 

1 . 0  per  cent  5 . 0  per  cent +  0 . 04  per  cent 

5 . 0  per  cent         10 . 0  per  cent ±  0 . 06  per  cent 

•       10 . 0  per  cent         30 . 0  per  cent ±  0 . 08  per  cent 

30 . 0  per  cent  upward ±  0 . 10  per  cent 

Applicability  of  the  Gravimetric  Method. — Satisfactory  results 
are  obtained  in  the  analysis  of  iron,  steel,  and  other  alloys  per- 
taining to  the  steel  industry. 


CHAPTER  IV 
PHOSPHORUS 

Phosphorus,  in  varying  quantities,  is  found  in  all  kinds  of  iron 
and  steel  as  well  as  in  the  various  alloys  used  in  steel  making. 
Sometimes  for  special  purposes,  iron-phosphorus  alloys  are  pre- 
pared containing  as  much  as  25  per  cent  of  phosphorus.  In 
materials  low  in  phosphorus  it  is  present  in  solid  solution  with 
the  iron  but  in  materials  rich  in  phosphorus  (over  1.7  per  cent 
P)  it  is  also  present  in  the  form  of  free  phosphide  of  iron. 

As  phosphorus  shows  a  marked  tendency  toward  segregation, 
it  is  necessary  to  exercise  particular  pains  in  selecting  the  sample 
for  analysis. 

All  methods  for  the  quantitative  determination  of  phosphorus 
in  iron  and  steel  are  based  upon  the  preliminary  oxidation  of  the 
phosphorus  to  phosphoric  acid.  Practically  all  phosphates, 
with  the  exception  of  sodium,  potassium  and  ammonium  phos- 
phates, are  insoluble  in  water  but  the  phosphoric  acid  obtained 
in  the  chemical  examination  of  iron  and  steel  is  usually  precipi- 
tated either  as  ferric  phosphate,  ammonium  phosphomolybdate 
or  as  magnesium  ammonium  phosphate. 

The  gravimetric  methods  are  based  upon  the  separation  of  the 
phosphoric  acid  from  at  least  the  greater  part  of  the  iron  by 
precipitation  as  ammonium  phosphomolybdate  or  as  ferric  phos- 
phate; in  the  latter  case,  the  greater  part  of  the  iron  is  kept  in  the 
ferrous  condition  and  separated  from  a  small  part  of  the  iron 
and  all  the  phosphorus  by  the  basic  acetate  method,  according 
to  which  a  precipitate  of  ferric  phosphate  and  basic  ferric  acetate 
is  formed.  The  ammonium  phosphomolybdate,  often  called 
''yellow  precipitate,"  is  sometimes  weighed  as  such  or  it  may  be 
dissolved  in  ammonium  hydroxide  solution  and  the  phosphorus 
precipitated  as  magnesium  ammonium  phosphate  which,  by 
ignition,  is  easily  changed  to  magnesium  pyrophosphate.  In 
the  basic  acetate  method,  the  precipitate  containing  all  of  the 
phosphorus  as  ferric  phosphate  is  dissolved  in  hydrochloric  acid, 

90 


PHOSPHORUS  91 

enough  tartaric  acid  is  added  so  that  insoluble  ferric  hydroxide 
or  phosphate  is  not  formed  upon  the  addition  of  ammonium 
hydroxide  and  the  phosphorus  is  then  precipitated  as  magnesium 
ammonium  phosphate.  In  all  the  well-known  gravimetric 
methods,  therefore,  the  phosphorus  is  weighed  as  ammonium 
phosphomolybdate  or  as  magnesium  pyrophosphate. 

The  best-known  volumetric  methods  are  based  on  the  proper- 
ties of  ammonium  phosphomolybdate.  The  molybdenum  con- 
tent of  this  precipitate  is  more  than  37  times  as  great  as  that  of 
the  phosphorus;  the  precipitate  when  dried  at  120°  contains 
approximately  1.63  per  cent  of  phosphorus.  The  volumetric 
methods  are  essentially  volumetric  ways  of  estimating  molyb- 
denum. They  depend  upon  the  fact  that  the  molybdic  acid  in 
the  yellow  precipitate  can  be  made  to  react  with  a  definite 
quantity  of  standard  caustic  alkali  solution  or  it  may  be  reduced 
to  a  lower  state  of  oxidation  and  be  then  oxidized  back  by  a 
definite  quantity  of  standard  oxidizing  agent. 

Many  years  of  experience  have  shown  that  the  so-called 
"rapid  methods"  are  just  as  accurate  as  the  longer  methods 
when  properly  carried  out  but  they  are  sensitive  to  slight  changes 
in  the  conditions  such  as  proper  temperature,  time  allowed  for 
the  completion  of  the  reaction,  concentration  and  acidity.  In 
the  methods  described  first,  it  will  be  assumed  that  the  original 
material  i?  sufficiently  soluble  in  acid  and  that  there  is  no  inter- 
fering element  present.  The  treatment  of  ferro-silicon,  iron 
phosphide  and  alloy  steels  will  be  discussed  later. 

1.  DETERMINATION  OF  PHOSPHORUS  IN  STEEL  BY  THE  MOLYB- 
DATE-MAGNESIA  METHOD 

Principle. — When  iron  or  steel  is  dissolved  in  nitric  acid 
(d.  1.21)  a  part  of  the  phosphorus  is  converted  into  phosphoric 
acid  but  the  remainder  is  left  in  solution  in  the  form  of  less 
highly  oxidized  acids,  such  as  phosphorous  acid.  In  order  that 
this  phosphorus  may  be  made  to  react  with  the  ammonium 
molybdate,  it  is  necessary  to  convert  it  into  phosphoric  acid  by 
means  of  a  more  energetic  oxidizing  agent  or  by  evaporating  to 
dryness  and  baking  the  residue. 

With  regard  to  the  completeness  of  the  precipitation  of  phos- 


92  CHEMICAL  ANALYSIS  OF  METALS 

phoric  acid  by  means  of  ammonium  molybdate  solution,  Hundes- 
hagen1  has  emphasized  the  following  facts: 

1.  Free  hydrochloric  and  sulfuric  acids,  or  too  concentrated 
nitric  acid,  prevent  the  complete  precipitation  of  the  phosphoric 
acid. 

2.  Small  quantities  of  free  nitric  acid  and  salts  of  monobasic 
acids  (chlorides,  bromides)  have  no  harmful  effect. 

3.  Ammonium  nitrate  has  a  marked  accelerating  effect  upon 
the  precipitation  of  ammonium  phosphomolybdate. 

Raising  the  temperature  also  hastens  the  formation  of  the 
precipitate  but  when  the  precipitation  takes  place  in  the  cold,  as 
recommended  by  Finkener,  there  is  less  danger  of  an  excess  of 
molybdic  acid  being  thrown  down;  this  is  important  in  all 
cases  where  the  precipitate  itself  is  to  be  weighed  or  the 
molybdenum  in  it  determined  as  a  measure  of  the  phosphorus 
content. 

When  arsenic,  tungsten  or  vanadium  is  present,  the  process 
which  is  to  be  described  first  cannot  be  used  without  modification. 

Solutions  Required. — Nitric  Acid. — Mix  1,000  c.c.  of  nitric 
acid,  d.  1.42  and  1,200  c.c.  of  distilled  water.  The  density 
of  the  diluted  acid  is  1.24  and  it  is  approximately  7-normal. 
Nitric  acid  of  this  concentration  is  prescribed  for  dissolving 
the  original  sample.  For  washing  the  ammonium  phosphomo- 
lybdate precipitate,  use  2  per  cent  nitric  acid  (prepared  by  mixing 
20  c.c.  of  nitric  acid,  d.  1.42  with  1,000  c.c.  of  distilled  water). 
Since  1  c.c.  of  the  original  nitric  acid  contains  approximately 
1  g.  of  dissolved  HN03  (1.42  X  69.8)  the  percentage  by  volume 
of  diluted  nitric  acid  is  practically  the  same  as  the  percentage 
by  weight;  this  is  not  true  of  the  other  common  acids. 

Potassium  Permanganate. — Dissolve  25  g.  of  permanganate  in 
1,000  c.c.  of  distilled  water. 

Ammonium  Bisulfite. — Dissolve  30  g.  of  ammonium  bisulfite 
in  1,000  c.c.  of  water  or  add  80  c.c.  of  6-normal  sulfurous  acid  to 
40  c.c.  of  6-normal  ammonium  hydroxide  and  dilute  the  mixture 
to  1,000  c.c. 

Ammonium  Hydroxide,  with  approximately  10  per  cent  NH3. 
Mix  1,000  c.c.  of  concentrated  ammonium  hydroxide,  d.  0.90,  with 
1,700  c.c.  of  distilled  water.  The  diluted  solution  has  a  density 

1  Z.  anal.  Chem.,  28,  141  (1889). 


PHOSPHORUS  93 

of  0.96  and  contains  9.90  per  cent  NH3by  weight;  it  is  commonly 
called  10  per  cent  ammonia.1 

Ammonium   Molybdate. — Solution   No.    1. — Place    100   g.    of 
"85  per  cent"  molybdic  acid  in  a  beaker,  mix  it  thoroughly 
with  240  c.c.  of  water  and  140  c.c.  of  ammonium  hydroxide,     . 
d.  0.90,  filter  and  add  60  c.c.  of  concentrated  nitric  acid,  d.  1.42, 
to  the  filtrate. 

Solution  No.  2. — Mix  400  c.c.  of  nitric  acid,  d.  1.42  and  960  c.c. 
of  water. 

When  the  solutions  are  cold,  add  solution  No.  1  to  solution 
No.  2  while  stirring  constantly;  then  add  0.1  g.  of  ammonium 
phosphate  dissolved  in  10  c.c.  of  distilled  water,  stir  and  let  the 
solution  stand  at  least  24  hr.  before  using. 

The  ammonium  molybdate  solution  should  be  kept  in  a  cool 
place  and  must  always  be  filtered  just  before  using.  The  solution 
works  well  when  freshly  prepared.  After  standing  a  few  months 
it  may  become  almost  worthless  as  a  precipitant. 

Magnesia  Mixture. — Dissolve  50  g.  of  anhydrous  magnesium 
chloride  or  110  g.  of  the  crystallized  salt  and  125  g.  of  ammonium 
chloride  in  750  c.c.  of  water  and  then  add  150  c.c.  of  ammonium 
hydroxide  d.  0.90.  The  presence  of  the  ammonium  chloride 
cuts  down  the  ionization  of  ammonium  hydroxide  to  such  an 
extent  that  magnesium  hydroxide  is  not  precipitated. 

Procedure. — Weigh  5  g.  of  steel  into  a  300-c.c.  Erlenmeyer 
flask  and  dissolve  in  75  c.c.  of  the  nitric  acid.  Heat  the  resulting 
solution  to  boiling  and,  while  boiling,  add  12  c.c.  0f  the  strong 
permanganate  solution.  Continue  boiling  until  manganese 
dioxide  precipitates.  Dissolve  the  precipitate  by  the  addition 
of  small  portions  of  ammonium  bisulfite  solution,  avoiding  an 
excess.  Boil  the  solution  until  it  is  clear  and  free  from  brown 
fumes,  cool  to  35°,  add  100  c.c.  of  the  ammonium  molybdate 
solution  at  room  temperature,  let  stand  1  min.,  shake  or  agitate 
for  3  min.  and  then  filter  on  a  9-cm.  paper  filter.  Wash  the 
precipitate  at  least  three  times  with  2  per  cent  nitric  acid  solution 
to  free  it  from  iron. 

Treat  the  precipitate  on  the  filter  with  the  10  per  cent  am- 
monium hydroxide  solution,  letting  the  solution  run  into  a  100- 
c.c.  beaker  containing  10  c.c.  of  concentrated  hydrochloric  acid 

1  Am.  Soc.  Testing  Materials,  1916,  211. 


94  CHEMICAL  ANALYSIS  OF  METALS 

and  0.5  g.  of  citric  acid;  add  30  c.c.  of  concentrated  ammonia 
solution  and  then  add  10  c.c.  of  the  magnesia  mixture  very  slowly 
while  stirring  vigorously.  Set  aside  in  a  cool  place  for  2  hr., 
filter  and  wash  with  the  10  per  cent  ammonium  hydroxide  solu- 
tion. Ignite  in  a  porcelain  crucible  and  weigh.  To  correct  for 
impurity,  dissolve  the  precipitate  of  magnesium  pyrophosphate  in 
5  c.c.  of  6-normal  nitric  acid  and  20  c.c.  of  distilled  water,  filter 
and  wash  the  residue  with  hot  water.  Ignite  and  weigh.  The 
difference  between  the  two  weights  represents  the  weight  of 
pure  magnesium  pyrophosphate;  it  contains  27.84  per  cent  of 
phosphorus. 

The  reactions  that  take  place  in  this  analysis  may  be  expressed 
by  the  following  equations: 

3Fe3P  +  41HN03-»9Fe(N03)3  +  14NO  +  3H3P04  +  16H2O 
H3P04   +  12(NH4)2Mo04  +  21HN03->(NH4)3P04-12Mo03  + 

21NH4NO8  +  12H2O 
(NH4)3PO4. 12MoO3  +  23NH4OH-»(NH4)2HP04  +  12(NH4)2 

MoO4  +  11H2O 

(NH4)2HPO4  +  MgCl2+NH4OH->MgNH4PO4  +  2NH4C1 +H2O 
2MgNH4PO4-+Mg2P2O7  +  2NH3  +  H20 

2.  DETERMINATION  OF  PHOSPHORUS  IN  STEEL  BY  THE  ALKALI- 
METRIC  METHOD1 

This  method  proposed  by  Hundeshagen  and  also  by  Manby 
was  subsequently  modified  by  J.  0.  Handy.  It  depends  upon 
the  fact  that  ammonium  phosphomolybdate  can  be  dissolved 
in  a  known  volume  of  standard  alkali  solution  and  the  excess 
of  the  latter  determined  by  titration  with  standard  nitric  acid 
using  phenolphthalein  as  indicator. 

Solutions  Required.— The  nitric  acid  for  dissolving  the  sample 
and  that  for  washing  the  yellow  precipitate,  the  potassium 
permanganate,  the  ammonium  bisulfite  and  the  ammonium 
molybdate  solutions  are  all  prepared  exactly  as  in  the  previous 
method. 

Potassium  Nitrate,  1  per  cent. — Dissolve  10  g.  of  the  salt  in 
1,000  c.c.  of  water. 

1  Am.  Soc.  Testing  Materials,  1916,  214. 


PHOSPHORUS  95 

Phenolphthalein  Indicator. — Dissolve  0.2  g.  in  50  c.c.  of  95 
per  cent  ethyl  alcohol  and  50  c.c.  of  water. 

Standard  Sodium  Hydroxide. — Dissolve  6.5  g.  of  pure  sodium 
hydroxide  in  1,000  c.c.  of  distilled  water,  add  a  slight  excess  of 
a  1  per  cent  solution  of  barium  hydroxide,  and  decant  off  the 
clear  solution  after  it  has  stood  over  night.  Standardize  the 
solution  against  a  steel  of  known  phosphorus  content,1  as  de- 
termined by  the  molybdate-magnesia  method,  and  adjust  the^ 
concentration  so  that  1  c.c.  =  0.01  per  cent  phosphorus  on  the 
basis  of  a  2-g.  sample.  Protect  the  solution  from  carbon  dioxide 
by  means  of  a  soda-lime  tube. 

Standard  Nitric  Acid. — Mix  10  c.c.  of  nitric  acid,  d.  1.42,  and 
1,000  c.c.  of  distilled  water.  Titrate  the  solution  against  the 
standard  sodium  hydroxide  and  adjust  the  concentration,  by 
adding  distilled  water,  until  the  two  solutions  are  equal. 

Sodium  hydroxide  absorbs  carbon  dioxide  from  the  atmosphere 
and,  with  phenolphthalein  in  the  cold,  one  molecule  of  carbon 
dioxide  neutralizes  as  much  sodium  hydroxide  as  one  molecule  of 
nitric  acid.  If  the  temperature  of  the  solution  is  raised  to  the 
boiling  point  and  an  excess  of  acid  is  added,  all  the  carbonic  acid 
is  expelled.  Consequently  it  is  essential  in  this  method  of 
analysis,  to  guard  against  the  absorption  of  carbon  dioxide  as 
much  as  possible,  to  always  titrate  at  the  same  temperature,  and 
to  carry  out  the  standardization  in  exactly  the  same  way  that 
the  analysis  is  made.  It  is  possible  to  compute  the  results  on 
the  basis  that  one  molecule  of  ammonium  phosphomolybdate 
reacts  with  23  molecules  of  sodium  hydroxide  (cf.  p.  94  where 
the  reaction  is  written  with  ammonium  hydroxide)  but  it  is  better 
to  standardize  against  a  steel  with  known  phosphorus  content. 

Procedure. — Dissolve  2.00  g.  of  steel  in  50  c.c.  of  the  nitric 
acid  using  a  300-c.c.  Erlenmeyer  flask.  Heat  the  solution  to 
boiling  and,  while  boiling,  add  about  6  c.c.  of  the  permanganate 
solution.  Continue  boiling  until  manganese  dioxide  precipi- 
tates and  dissolve  the  precipitate  by  additions  of  the  ammonium 
bisulfite  solution.  Boil  until  the  solution  is  clear  and  free  from 
brown  fumes,  cool  to  80°,  add  50  c.c.  of  the  ammonium  molybdate 
at  room  temperature,  let  stand  1  min.,  shake  or  agitate  for  3  min., 
and  filter  on  a  9  cm.  filter.  Wash  the  precipitate  three  times 

1  Bureau  of  Standards  Steel  No.  19  (a)  is  recommended. 


96  CHEMICAL  ANALYSIS  OF  METALS 

with  the  2  per  cent  nitric  acid  to  free  it  from  iron  and  then  with 
1  per  cent  potassium  nitrate  solution  until  the  precipitate  and 
flask  are  free  from  acid. 

Transfer  the  paper  and  precipitate  back  to  the  original  flask, 
add  20  c.c.  of  water  free  from  carbon  dioxide,  3  drops  of  phe- 
nolphthalein  solution  as  indicator  and  an  excess  of  standard 
sodium  hydroxide  solution.  Insert  a  rubber  stopper  in  the 
neck  of  the  flask  and  shake  vigorously  until  all  the  precipitate 
Dissolves.  Wash  off  the  stopper,  rinse  the  sides  of  the  flask  with 
distilled  water  and  determine  the  excess  of  sodium  hydroxide 
by  titration  with  standard  nitric  acid  solution. 

Computation. — If  the  two  standard  solutions  are  exactly  the 
recommended  strength,  the  per  cent  phosphorus  is  found  by 
subtracting  the  volume  of  nitric  acid  used  from  the  total  volume 
of  sodium  hydroxide  solution  and  moving  the  decimal  point  two 
places  to  the  left.  If  both  solutions  are  exactly  tenth-normal, 

(c.c.  NaOH  -  c.c.  HNO3)  X  0.01348 
Per  cent  P  =  -  — -—    — j— 

wt.  ot  sample 

V 

3.  DETERMINATION  OF  PHOSPHORUS  IN  CAST  IRON* 

The  determination  of  phosphorus  in  cast  iron  often  causes 
trouble,  particularly  when  titanium  is  present.  The  solutions 
required  in  this  method  of  analysis  are  the  same  as  given  under 
the  two  methods  already  described. 

Procedure  for  Non-titaniferous  Irons. — Weigh  1.00  of  the 
iron,  or  twice  as  much  if  the  metal  is  low  in  phosphorus,  into  a 
400-c.c.  beaker  and  dissolve  in  25  (or  50)  c.c.  of  nitric  acid. 
Evaporate  to  dryness  and  heat  on  the  hot  plate,  or  in  an  air  bath, 
at  approximately  200°  for  about  an  hour.  This  baking  of  the 
ferric  nitrate  accomplishes  the  same  effect  as  the  addition  of 
permanganate  in  the  analysis  of  steel  by  the  preceding  methods. 
Allow  the  beaker  to  cool  and  heat  with  15  c.c.  of  concentrated 
hydrochloric  acid  until  the  iron  oxide  has  all  dissolved  and  then 
evaporate  to  dryness  to  render  the  silica  insoluble.  Redissolve 
in  15  c.c.  of  concentrated  hydrochloric  acid,  dilute  with  water, 
filter  off  the  insoluble  silicious  residue  and  wash  the  filter  several 
times  with  dilute  hydrochloric  acid  and  then  with  water. 
lAm.  Soc.  Testing  Materials,  1915,  525. 


PHOSPHORUS  97 

This  residue  often  contains  a  little  phosphorus.  To  recover 
it,  burn  off  the  filter  paper  and  the  graphite  by  heating  in  a 
platinum  crucible.  Cool,  add  a  few  cubic  centimeters  of  hydro- 
fluoric acid  and  a  drop  of  sulfuric  acid  and  evaporate  off  all  the 
silicon  fluoride  and  excess  hydrofluoric  acid  but  stop  heating 
before  all  the  sulfuric  acid  is  expelled.  Take  up  the  residue  in 
a  little  concentrated  hydrochloric  acid,  dilute  and  filter  into  the 
original  solution. 

Evaporate  now  to  a  small  volume  until  salts  just  begin  to 
separate.  Add  10  c.c.  of  concentrated  nitric  acid  and  again 
evaporate  to  small  volume,  add  15  c.c.  more  of  concentrated 
nitric  acid  and  once  more  evaporate.  Then,  with  the  solution 
in  an  Erlenmeyer  flask  at  a  volume  of  not  more  than  25  c.c.,  add 
25  to  100  c.c.  of  ammonium  molybdate  reagent,  according  to  the 
phosphorus  content.  Shake  the  solution  for  4  or  5  min.  and  allow 
the  contents  of  the  flask  to  stand  for  30  min.  (but  not  more  than 
4  hr.)  at  room  temperature. 

Three  methods  of  treating  the  ammonium  phosphomolybdate 
precipitate  are  recommended  by  the  American  Society  of  Testing 
Materials,  either  one  of  which  should  give  good  results. 

(a)  Filter  into  a  weighed  Gooch  crucible,  wash  the  precipitate 
once  or  twice  with  ammonium  molybdate  reagent  diluted  with 
an  equal  volume  of  water  and  then  with  1  per  cent  nitric  acid 
four  times.  Dry  1  hr.  at  120°  and  assume  that  the  precipitate 
contains  1.63  per  cent  phosphorus. 

(6)  Filter  the  solution  through  a  9-cm.  paper  filter  and  deter- 
mine the  phosphorus  by  the  alkalimetric  method  described  on 
page  94. 

(c)  Filter  the  solution  through  a  small  paper  filter  and  deter- 
mine the  phosphorus  as  described  on  page  91. 

Basic  Acetate  Procedure  for  Irons  Containing  Titanium. — The 
method  of  treatment  is  the  same  as  recommended  for  the  analysis 
of  nontitaniferous  irons  down  to  the  point  where  the  residue  from 
hydrofluoric  acid  treatment  is  dissolved  and  added  to  the  main 
solution.  After  this  has  been  done,  heat  the  entire  solution  to 
boiling  and  add  gradually  from  a  small  beaker  a  mixture  of  2  c.c. 
ammonium  acid  sulfite  solution  (made  by  saturating  concentrated 
ammonia  solution  with  sulfur  dioxide  gas)  and  10  c.c.  of  strong 
ammonia.  The  precipitate  which  forms  at  first,  redissolves.  If 

7 


98  CHEMICAL  ANALYSIS  OF  METALS 

at  any  time  while  adding  the  sulfite  solution  the  precipitate 
will  not  dissolve,  even  upon  stirring  vigorously,  add  a  few  drops 
of  hydrochloric  acid  and,  after  the  solution  clears,  continue  the 
addition,  very  slowly,  of  the  ammonium  acid  sulfite  solution. 
When  all  but  a  little  of  the  reagent  has  been  added,  replace  the 
beaker  over  the  flame.  Finally  add  to  the  hot  solution  ammo- 
nium hydroxide,  drop  by  drop,  until  the  solution  is  quite  decolor- 
ized and  a  little  more  ammonia  causes  a  slight  greenish  precipitate 
to  remain  undissolved  even  after  stirring.  Now  add  the  remainder 
of  the  sulfite  solution;  this  should  throw  down  a  white  precipitate 
(titanium  hydroxide)  which  usually  redissolves  leaving  the 
solution  quite  clear  and  nearly  colorless.  If  a  precipitate 
remains,  add  hydrochloric  acid,  drop  by  drop,  until  the  solution 
clears;  it  should  smell  perceptibly  of  sulfur  dioxide. 

If  the  solution  of  ammonium  acid  sulfite  was  too  weak,  the 
desired  reduction  of  the  ferric  chloride  will  be  incomplete  and 
there  will  be  no  odor  of  sulfur  dioxide  on  adding  acid.  In  such  a 
case  add  more  acid  ammonium  sulfite  (without  the  addition  of 
ammonia)  until  the  solution  smells  strongly  of  sulfur  dioxide,  then 
add  ammonia  solution  until  a  slight  permanent  precipitate  is 
formed  and  redissolve  it  in  as  little  hydrochloric  acid  as  possible. 

At  this  point,  the  solution  should  be  very  nearly  neutral,  all  of 
the  iron  should  be  in  the  ferrous  condition  and  a  slight  excess  of 
sulfurous  acid  should  be  present.  Add  5  c.c.  of  concentrated 
hydrochloric  acid  to  make  it  decidedly  acid  and  to  insure  the 
complete  decomposition  of  any  excess  ammonium  sulfite  that  may 
be  present.  Boil  the  solution,  while  passing  a  stream  of  carbon 
dioxide  through  it,  until  every  trace  of  sulfurous  acid  is  expelled. 
(If  arsenic  is  present,  pass  a  current  of  hydrogen  sulfide  through 
the  solution  for  15  min.,  filter  off  the  arsenic  sulfide  and  expel  the 
excess  of  precipitant  while  passing  a  current  of  carbon  dioxide 
through  the  boiling  liquid.) 

The  next  step  is  to  provide  enough  ferric  ions  to  combine  with 
all  the  phosphorus.  This  may  be  accomplished  by  adding  a  few 
drops  of  bromine  water  to  the  solution  or  by  adding  a  little  pure 
ferric  chloride  solution.  After  this  has  been  done,  cool  the  solu- 
tion by  placing  the  flask  in  cold  water  and  slowly  add  ammonia 
solution,  drop  by  drop  at  the  last,  with  constant  stirring.  The 
green  precipitate  of  ferrous  hydroxide  which  is  seen  at  first  is 


PHOSPHORUS  99 

dissolved  by  stirring,  leaving  the  solution  clear.  Subsequently, 
although  the  green  precipitate  redissolves,  a  whitish  one  of  titan- 
ium hydroxide  and  ferric  phosphate  remains  and  the  next  drop 
gives  a  distinct  reddish  tint  to  the  precipitate.  Then,  another 
of  ammonia  makes  the  whole  precipitate  appear  green.  If, 
before  this  occurs,  the  whole  precipitate  does  not  appear  decid- 
edly red  in  color,  showing  that  a  slight  excess  of  ferric  iron  was 
present,  dissolve  the  green  precipitate  with  a  drop  or  two  of 
hydrochloric  acid,  add  a  little  bromine  water  or  1  or  2  c.c.  of  dilute 
ferric  chloride  solution,  and  then  treat  with  ammonia  as  before 
until  a  reddish  precipitate  is  obtained  before  the  green  coloration 
appears.  At  this  point  the  precipitate  contains  all  the  phos- 
phorus as  ferric  phosphate  together  with  a  small  amount  of  basic 
ferric  salt  and  enough  ferrous  hydroxide  to  give  a  green  color. 

Dissolve  the  green  ferrous  precipitate  by  a  few  drops  of  acetic 
acid,  sp.  gr.  1.04,  and  the  remaining  precipitate  should  be  dis- 
tinctly red  in  color.  Add  about  1  c.c.  of  acetic  acid  in  excess  and 
dilute  the  solution  with  boiling  water  so  that  the  400-c.c.  beaker 
is  about  four-fifths  full.  Boil  the  solution  1  min.  and,  while 
keeping  the  liquid  hot,  filter  as  rapidly  as  possible  through  a  14- 
cm.  filter  and  wash  once  with  hot  water.  The  filtrate  should  run 
through  clear  at  first  but  should  become  cloudy  owing  to  the  grad- 
ual oxidation  of  some  of  the  ferrous  salt  which  precipitates  as 
basic  ferric  acetate. 

Dry  the  precipitate  on  the  filter  without  scorching  the  latter. 
Remove  with  filter  paper  any  precipitate  that  may  adhere  to 
the  beaker  and  dry  this  paper  also.  Transfer  the  main  portion 
of  the  precipitate  to  a  small  porcelain  mortar.  Carefully  burn 
the  filter  papers  and  transfer  the  ash  to  the  mortar.  Triturate 
the  ferric  phosphate  and  basic  ferric  acetate  with  3  g.  of  anhy- 
drous sodium  carbonate  and  a  little  potassium  nitrate.  Transfer 
the  mixture  to  a  platinum  crucible,  cleaning  mortar  and  pestle 
with  a  little  more  sodium  carbonate,  and  fuse  the  mass  for  J£  hr. 
Cool,  dissolve  the  fused  mass  in  hot  water,  filter  and  wash  with 
hot  water.  The  residue  on  the  filter  will  contain  nearly  all  the 
titanium  and  the  aqueous  extract  will  contain  all  the  phosphorus 
or  sodium  phosphate. 

Acidify  the  alkaline  solution  with  nitric  acid,  evaporate  nearly 
to  dry  ness  in  a  small  casserole,  transfer  to  an  Erlenmeyer  flask 


100  CHEMICAL  ANALYSIS  OF  METALS 

and,  with  the  volume  not  more  than  25  c.c.,  precipitate  at  room 
temperature  with  25  to  100  c.c.  of  the  molybdate  reagent.  From 
this  point  the  procedure  is  the  same  as  for  non-titaniferous  irons. 

4.  DETERMINATION  OF  PHOSPHORUS 

BY  METHOD  OF  C.  M.  JOHNSON1 

All  of  the  methods  described  thus  far  have  called  for  the  use  of 
an  acid  solution  of  ammonium  molybdate.  Such  a  solution 
becomes  turbid  on  standing  and  its  precipitating  power  is  con- 
tinuously lessejied.  Johnson  has  found  it  advantageous  to  use 
a  faintly  ammoniacal  solution  of  ammonium  molybdate  as  reagent 
and  has  succeeded  in  modifying  the  conditions  of  precipitation  so 
that  the  determination  of  phosphorus  in  materials  containing 
vanadium  is  much  easier  than  according  to  the  methods  formerly 
used. 

The  solutions  required,  except  as  indicated  in  the  directions, 
are  the  same  as  recommended  in  the  methods  already  described, 
with  the  exception  of  the  ammonium  molybdate  reagent. 

Ammonium  Molybdate  Solution. — Into  each  of  four  800-c.c. 
beakers  weigh  55  g.  of  ammonium  molybdate  and  50  g.  of  ammo- 
nium nitrate  and  add  40  c.c.  of  ammonium  hydroxide,  d. 
0.96.  Dilute  the  contents  of  each. beaker  with  enough  water  to 
make  the  total  volume  700  c.c.  Heat  for  about  30  min.  and  stir 
occasionally  until  all  the  salts  have  dissolved.  Combine  the 
contents  of  the  four  beakers  by  pouring  into  a  large  bottle,  dilute 
to  4,000  c.c.  and  allow  to  stand  over  night.  Filter  the  next  morn- 
ing through  double  15-cm.  filters  but  do  not  wash  the  residue. 

Procedure  for  Non-vanadium  Steels  and  Cast  Irons.— Weigh 
1.63  g.  of  the  iron  or  steel  into  a  150-c.c.  beaker  and  dissolve  in 
45  c.c.  of  25  per  cent  nitric  acid,  heating  the  contents  of  the 
beaker  over  a  small  flame.  (If  an  insoluble  residue  remains 
filter  it  off  and  treat  with  HF,  etc.,  as  described  in  Method  3, 
finally  concentrating  the  solution  to  45  c.c.) 

Add  about  6  c.c.  of  strong  permanganate  solution  and  clear  the 
solution  as  described  in  Methods  1  and  2.  After  boiling  off 
the  brown  fumes,  add  15  c.c.  of  concentrated  nitric  acid,  rinse 

1J.  /.  E.  C.,  11,  113  (1919). 


•  >/  (\        i  V  \    f,       101 

down  the  cover  glass  and  sides  of  the  beaker  and  add  50  c.c.  of 
ammonium  molybdate  reagent.  Stir  briskly  (about  2  min.), 
until  the  precipitate  is  formed  completely,  allow  to  stand  20  min. 
and  filter  through  a  7-cm.  filter.  Wash  five  times  with  2  per 
cent  nitric  acid  and  then  with  1  per  cent  potassium  nitrate 
solution  until  the  outside  fold  of  the  filter  has  no  sour  taste. 
With  high  phosphorus  content  this  may  take  35  or  40  washings. 
Continue  the  analysis  as  in  Method  2. 

If  the  steel  contains  2.5  per  cent  vanadium  or  less,  good  results 
are  obtained  by  practically  the  same  procedure  except  that  just 
before  adding  the  ammonium  molybdate,  40  to  50  c.c.  of  nitric 
acid  are  added  instead  of  15  c.c. 

Procedure  for  Steels  Containing  More  Than  2.5  Per  Cent  Vana- 
dium.— Digest  1  g.  of  steel  in  a  covered,  250-c.c.  porcelain  dish 
with  a  mixture  of  30  c.c.  concentrated  hydrochloric  acid  and  an 
equal  volume  of  concentrated  nitric  acid.  After  heating  about  an 
hour,  remove  the  cover  glass,  rinse  off  the  bottom,  and  add  100 
c.c.  of  concentrated  nitric  acid.  Evaporate  the  solution  to  dry- 
ness  and  bake  5  min.  at  200°.  Cool,  dissolve  the  oxides  in  35  c.c. 
of  concentrated  hydrochloric  acid,  evaporate  to  10  c.c.,  add  50 
c.c.  of  concentrated  nitric  acid,  again  evaporate  to  10  c.c.,  add 
10  c.c.  more  of  nitric  acid  and  heat  a  short  time  with  the  dish 
covered.  Filter  through  an  asbestos  pad  on  glass  wool  (cf. 
Volhard  method  for  manganese)  and  catch  the  filtrate  in  a  150-c.c. 
beaker.  Wash  the  vanadium  oxide  residue  15  times  with  small 
portions  of  a  solution  containing  200  c.c.  of  concentrated  nitric  acid, 
100  c.c.  of  water  and  20  g.  of  ferric  nitrate  free  from  phosphorus. 

Concentrate  the  filtrate  to  10  c.c.  and  filter  off  a  second  crop  of 
vanadic  acid  anhydride.  A  third  evaporation  of  the  filtrate 
should  show  no  further  deposition  of  vanadic  acid  anhydride. 
Add  40  c.c.  of  concentrated  nitric  acid  and  50  c.c.  of  ammonium 
molybdate.  Filter,  wash  and  analyze  the  precipitate  as  indi- 
cated above. 

5.  DETERMINATION  OF  PHOSPHORUS  BY  THE  ACETATE 
METHOD  OF  A.  A.  BLAIR  (MODIFIED) 

The  method  is  in  principle  the  same  as  that  recommended 
for  the  determination  of  phosphorus  in  cast  irons  containing 
titanium. 


102 


OF  METALS 


Procedure. — Dissolve  5  g.  of  borings  in  80  c.c.  of  nitric  acid 
(d.  1.2)  and  when  the  reaction  begins  to  slacken  add  10  c.c.  of 
strong  hydrochloric  acid.  Evaporate  to  dryness  and  bake  until 
the  nitrates  are  decomposed  in  order  to  oxidize  all  the  phosphorus 
to  phosphoric  acid.  Cool,  add  30  c.c.  of  concentrated  hydro- 
chloric acid,  heat  until  the  ferric  oxide  has  all  dissolved  and 
again  evaporate  to  dryness  but  without  baking  the  residue. 
Cool,  dissolve  in  30  c.c.  strong  hydrochloric  acid,  dilute  and 
filter  off  the  silica  (cf.  p.  104). 

Dilute  the  filtrate  from  the  silica  to  about  400  c.c.  and  add 
ammonia  until  a  slight  permanent  precipitate  of  ferric  hydroxide 
is  formed.  Add  200  c.c.  of  a  saturated  aqueous  solution  of  sulfur 
dioxide  and  slowly  heat  to  boiling.  The  precipitate  soon  dis- 
solves and  the  liquid  assumes  a  dark  reddish  brown  color,  which, 
on  further  heating,  becomes  light  green  or  nearly  colorless.  As 
soon  as  this  point  is  reached,  add  10  to  20  c.c.  of  concentrated 
hydrochloric  acid  and  introduce  carbon  dioxide  gas  until  the 
excess  of  sulfur  dioxide  is  expelled.  Cool  the  solution  by  placing 
the  beaker  in  cold  water,  add  1  or  2  c.c.  of  chlorine  or  bromine 
water  to  oxidize  a  little  of  the  iron,  and  ammonia  very  care- 
fully, with  constant  stirring,  until  the  greenish  precipitate  of 
ferrous-ferric  hydroxide  dissolves  with  difficulty.  Continue  the 
addition  of  ammonia,  drop  by  drop,  until  a  distinct  brown  pre- 
cipitate is  formed  which  becomes  green  on  stirring.  If,  before 
this  occurs,  the  precipitate  does  not  appear  decidedly  red  in 
color,  dissolve  it  with  a  drop  or  two  of  hydrochloric  acid,  add  a 
little  more  chlorine  or  bromine  water  and  repeat  the  addition  of 
ammonia  until  a  reddish  brown  precipitate  is  obtained  and  then 
the  green  coloration.  Ferric  phosphate  being  white,  the  forma- 
tion of  a  red  precipitate  shows  that  there  are  more  ferric  ions 
present  than  are  required  to  unite  with  all  the  phosphoric 
acid.  Now  add  acetic  acid  (d.  1.04),  drop  by  drop,  until 
the  green  part  of  the  precipitate  redissolves  leaving  a  reddish 
precipitate  behind,  add  about  1  c.c.  of  acetic  acid  more,  heat 
to  boiling  and  keep  at  this  temperature  for  1  min.  All  the 
phosphorus  is  then  precipitated  as  ferric  phosphate  and  some  of 
the  iron  is  precipitated  as  basic  ferric  acetate,  but  the  greater 
part  of  the  iron  remains  in  solution  in  the  ferrous  state  Filter 
through  a  large  filter  and  wash  the  precipitate  once  with  hot 


PHOSPHORUS  103 

water.     The  filtrate  is  at  first  clear,  but  becomes  turbid  on  stand- 
ing in  the  air,  owing  to  oxidation  of  the  ferrous  ions. 

Dissolve  the  precipitate  adhering  to  the  sides  of  the  beaker  by 
warming  it  with  about  15  c.c.  of  hydrochloric  acid  (1  vol.  cone, 
acid:  1  vol.  water)  and  add  10  c.c.  of  bromine  water.  If  necessary, 
add  a  few  drops  more  of  concentrated  hydrochloric  acid  to 
complete  the  solution  of  the  precipitate.  Pour  the  acid  solu- 
tion through  the  filter  and  catch  the  filtrate  in  a  small  beaker. 
Wash  the  filter  well  with  hot  water  and  evaporate  the  solution 
nearly  to  dryness  to  expel  the  excess  of  hydrochloric  acid.  Add 
a  filtered  solution  of  5  or  10  g.  of  citric  acid  dissolved  in  10  or 
20  c.c.  of  water,  also  10  c.c.  of  magnesia  mixture1  and  enough 
ammonia  to  make  the  solution  faintly  alkaline.  When  perfectly 
cold,  add  one-half  the  liquid's  volume  of  strong  ammonia  and  stir 
well.  After  standing  12  hr.,  filter  off  the  precipitate  of  magne- 
sium ammonium  phosphate  and  wash  it  with  2.5  per  cent 
ammonia  containing  2.5  g.  of  ammonium  nitrate  in  100  c.c. 
Dissolve  the  precipitate  in  hydrochloric  acid,  evaporate  to  dry- 
ness  to  remove  silica  obtained  from  the  reagents  and  the  glass, 
moisten  the  residue  with  a  little  hydrochloric  acid,  take  up  with  a 
little  water  and  filter  through  a  small  filter.  To  the  filtrate, 
which  should  not  be  over  20  c.c.  at  the  most,  add  1  c.c.  of  the  50 
per  cent  citric  acid  solution,  2  drops  of  magnesia  mixture  and 
reprecipitate  the  phosphorus  in  the  same  way  as  before.  In  this 
way  a  precipitate  is  obtained  which  yields  pure  magnesium 
pyrophosphate  upon  ignition. 

Computation. — If  p  is  the  weight  of  ignited  precipitate,  and  s 
the  weight  of  sample  taken,  then 

2P       100      27.87p 

TVT — TTFT" =  ~        —  =   Per 

Mg2P2O7      S  S 

REMARKS. — Blair  recommends  the  use  of  ammonium  bisulfite 
instead  of  sulfurous  acid  for  the  reduction  of  the  ferric  salt. 
Commercial  ammonium  bisulfite  sometimes  contains  phosphoric 
acid  so  that  it  seems  safer  to  recommend  sulfurous  acid  itself. 
Again,  Blair  suggests  that  hydrogen  sulfide  be  passed  into  the 
solution  after  the  excess  of  sulfur  dioxide  has  been  removed,  in 

1  Dissolve  55  g.  MgCl2.6H2O,  and  70  g.  NH4C1  in  water  containing  a  little 
hydrochloric  acid,  add  250  c.c.  of  ammonia  (d.  0.96),  and  dilute  to  1  liter. 
Filter  after  the  solution  has  stood  several  days. 


104  CHEMICAL  ANALYSIS  OF  METALS 

order  to  precipitate  any  arsenic  as  the  trisulfide.  Unless  this  is 
done  some  arsenic  is  likely  to  be  precipitated  with  the  phosphorus. 
The  filtrate  from  the  hydrogen  sulfide  precipitation  is  heated  to 
boiling,  the  excess  of  hydrogen  sulfide  expelled  by  means  of  a 
stream  of  carbon  dioxide,  and  the  solution  then  partly  oxidized 
as  described  above. 

If  the  material  analyzed  contains  titanium,  a  compound  con- 
taining titanic  acid,  ferric  oxide  and  phosphoric  acid  is  present  in 
the  insoluble  residue  obtained  after  evaporating  the  original  solu- 
tion to  dryness.  This  residue  should  be  filtered  off,  ignited  and 
treated  with  sulfuric  and  hydrofluoric  acids  to  remove  the  silica. 
After  evaporating  off  the  excess  of  sulfuric  acid,  fuse  the  residue 
with  sodium  carbonate  and  extract  the  fused  mass  with  water. 
Acidify  the  aqueous  solution  with  hydrochloric  acid  and  add  it  to 
the  main  solution. 

Another  difficulty  that  is  likely  to  be  encountered  when 
titanium  is  present,  is  the  formation  of  the  above-mentioned 
insoluble  compound  when  the  solution  obtained  by  dissolving  the 
acetate  precipitate  is  being  concentrated.  To  avoid  this,  the 
evaporation  must  be  watched  carefully  and  citric  acid  added 
as  soon  as  any  titanic  acid  begins  to  separate. 

6.  DETERMINATION  OF  PHOSPHORUS  BY  PERMANGANATE 
TITRATION 

This  method  was  recommended  some  years  ago  by  a  com- 
mittee of  American  chemists  consisting  of  W.  P.  Barba,  A.  A. 
Blair,  T.  M.  Drown,  C.  B.  Dudley  and  P.  W.  Shinier.  It  gives 
accurate  results  when  the  prescribed  conditions  are  carefully 
maintained.  It  depends  upon  the  precipitation  of  the  phos- 
phorus as  ammonium  phosphomolybdate  under  conditions  such 
that  the  ratio  of  P:Mo  =  1:12  is  maintained,  the  dissolving  of 
the  precipitate  in  dilute  ammonia,  acidification  with  sulfuric 
acid,  reduction  of  the  molybdenum  by  zinc  and  titration  back  to 
the  hexavalent  condition  by  means  of  potassium  permanganate. 

Reagents  Required. — Directions  for  preparing  solutions  of 
ammonium  molybdate,  25  per  cent  nitric  acid,  10  per  cent 
ammonia  solution,  and  strong  permanganate  were  given  in 
Methods  1  and  2.  The  other  solutions  required  are: 


PHOSPHORUS 


105 


Dilute  Sulfuric  Acid. — Add  25  c.c.  of  concentrated  acid  to 
1  liter  of  water. 

Acid  Ammonium  Sulfate. — To  1  liter  of  water  add  15  c.c. 
of  concentrated  ammonia  and  25  c.c.  of  concentrated  sulfuric 
acid  and  stir  well. 

Standard  Permanganate  Solution. — Dissolve  about  2  g.  of 
potassium  permanganate  crystals  for  each  liter  of  solution 
desired.  In  order  that  the 
solution  may  keep  well,  it  is 
best  to  use  the  same  care 
in  preparing  it  as  described 
on  p.  57. 

Any  good  method  of 
standardizing  a  perman- 
ganate solution  is  perfectly 
satisfactory.  It  is  a  very 
common  practice,  however, 
to  use  metallic  iron  wire 
for  this  purpose;  such  a 
method  will  be  described 
and  it  involves  the  use  of 
the  Jones  reductor,  which 
is  also  recommended  for 
use  in  the  phosphorus  de- 
termination. 

The  Jones  reductor,  Fig. 

18,  consists  of  a  glass  tube  A 

'  i  j     vu  FlG-  18- 

about  30  cm.  long  and  with 

an  inside  diameter  of  about  18  mm.;  at  the  bottom  of  the 
tube  a  piece  of  platinum  gauze  is  placed  or  some  glass  beads. 
Then  follows  a  plug  of  glass  wool  and  a  thin  layer  of  asbestos 
such  as  is  used  for  Gooch  crucibles.  The  layer  of  asbestos 
on  the  glass  wool  should  be  somewhat  less  than  1  mm. 
in  thickness.  If  too  little  asbestos  is  used,  the  zinc  will  pass 
through  into  the  flask  and  cause  trouble  in  the  subsequent 
titration.  Too  thick  a  layer,  on  the  other  hand,  soon  becomes 
clogged  and  the  liquid  will  pass  through  too  slowly.  The  tube 
is  finally  filled  with  amalgamated  zinc  to  within  5  cm.  of  the  top 
and  on  the  zinc  is  placed  a  little  glass  wool  to  act  as  a  filter. 


tion 


106  CHEMICAL  ANALYSIS  OF  METALS 

The  amalgamated  zinc  is  prepared  by  taking  some  granu- 
lated zinc  which  will  pass  through  a  20-mesh  sieve  but  not 
through  a  30-mesh,  cleaning  it  with  a  little  hydrochloric  acid 
and  adding  mercuric  chloride  solution  until  hydrogen  ceases  to 
be  evolved. 

Amalgamated  zinc  is  just  as  efficient  as  pure  zinc  with  regard  to 
its  reducing  power  upon  ferric  salts  or  upon  molybdic  acid  but  it 
does  not  dissolve  readily  in  dilute  sulfuric  acid.  For  this  reason 
the  desired  reduction  can  be  accomplished  by  passing  the  solu- 
tion through  the  tube  which  would  be  impossible  with  ordinary 
zinc  on  account  of  the  lively  evolution  of  hydrogen.  Before 
using  a  Jones  reductor  after  it  has  been  standing  for  some  time 
it  should  be  washed  well  with  dilute  sulfuric  acid. 

In  running  a  blank,  i.e.,  an  experiment  with  the  same  quan- 
tities of  acid  and  wash  water  as  are  to  be  used  in  the  analysis  or 
standardization,1  and  in  all  determinations,  proceed  as  follows: 

Pour  100  c.c.  of  hot,  2.5  per  cent  sulfuric  acid  into  the  funnel  B 
which  forms  the  top  of  the  reduction  tube,  open  the  stopcock  C 
and  apply  gentle  suction.  When  only  a  little  dilute  acid  remains 
in  the  funnel,  add  the  solution  to  be  reduced  (50  c.c.  of  water, 
10  c.c.  of  concentrated  sulfuric  acid  and  5  c.c.  of  dilute  am- 
monia in  the  case  of  blanks)  and  follow  it  with  250  c.c.  of  hot 
dilute  sulfuric  acid  (with  which  the  original  beaker  is  washed  in 
several  portions)  and  100  c.c.  of  water.  Air  should  not  be  allowed 
to  enter  the  reductor  at  any  time  by  letting  all  the  acid  or  water 
run  out  of  the  funnel,  B.  Before  starting  any  analysis  a  blank 
should  be  run  and  the  volume  of  permanganate  required  should 
not  be  over  0.2  c.c.,  as  a  rule.  If  more  is  required  the  blank  test 
should  be  repeated. 

STANDARDIZATION  OF  PERMANGANATE  SOLUTION  BY  MEANS 
OF  IRON  WIRE 

Dissolve  about  0.2  g.  of  standard  wire  in  a  125-c.c.  Erlenmeyer 
flask  containing  30  c.c.  of  water  and  10  c.c.  of  concentrated  sul- 
furic acid.  When  the  iron  has  all  dissolved,  boil  the  solution 

1  This  is  necessary  on  account  of  the  iron,  sulfur,  etc.,  which  the  zinc 
contains.  An  allowance  should  be  made  for  these  impurities  whenever 
zinc  is  used  as  a  reducing  agent. 


PHOSPHORUS  107 

gently  for  a  few  moments  in  order  to  expel  hydrocarbons.1  Pass 
the  solution  through  the  reductor,  in  the  manner  already  de- 
scribed, and  titrate  slowly  with  the  potassium  permanganate  solu- 
tion. Duplicate  results  in  a  standardization  should  agree  within 
3  parts  in  one  thousand.  Greater  precision  is  unnecessary  in  the 
analysis  of  iron  or  steel  for  phosphorus. 

Analysis  of  Steel. — Weigh  about  2  g.  of  borings  into  a  250-c.c. 
Erlenmeyer  flask,  add  100  c.c.  of  dilute  nitric  acid  (d.  1.13)  and 
insert  a  small  funnel  in  the  neck  of  the  flask.  Heat  until  the  sam- 
ple is  all  dissolved  and  the  oxides  of  nitrogen  are  no  longer  visible 
in  the  flask.  Add  10  c.c.  of  the  strong  permanganate  solution,  or 
more  if  necessary  to  impart  a  strong  pink  color  to  the  solution. 
Boil  until  the  pink  color  disappears  and  manganese  dioxide  is 
precipitated.  Continue  boiling  for  several  minutes,  then  remove 
from  the  source  of  heat  and  add  a  few  drops  of  sulfurous  acid,  a 
small  crystal  of  ferrous  sulfate,  or  a  solution  of  0.5  g.  sodium 
thiosulfate  in  10  c.c.  of  water,  and  repeat  the  addition  of  reduc- 
ing agent  at  short  intervals  until  all  the  manganese  dioxide  has 
dissolved.2  Boil  2  min.  longer  and  then  cool  by  placing  the 
flask  in  cold  water  or  by  allowing  it  to  stand  in  the  air  until  it 
feels  cool  to  the  hand.  Add  carefully  40  c.c.  of  dilute  ammonia 
and  rotate  the  flask  until  the  precipitated  ferric  hydroxide  all  dis- 
solves and  a  pale  yellow  solution  is  obtained.  When  the  solution 
is  at  about  35°  ,  add  40  c.c.  of  ammonium  molybdate  solution, 
close  the  flask  with  a  rubber  stopper  and  shake  for  5  min.  Allow 
the  precipitate  to  settle  for  a  few  minutes  and  filter.  Wash  the 
precipitate  several  times  by  decantation  and  then  on  the  filter 
with  acid  ammonium  sulfate  solution  until  2  or  3  c.c.  of  the  filtrate 
give  no  reaction  for  molybdenum  when  tested  with  yellow  ammo- 
nium sulfide.  It  is  best  to  compare  the  test  with  a  blank  made 
by  adding  some  of  the  wash  liquid  itself  to  a  drop  of  yellow  ammo- 
nium sulphide  solution.  When  iron  is  present  a  black  precipi- 
tate is  obtained  while  the  test  solution  is  still  ammoniacal,  but 

1  Many  chemists  oxidize  the  carbonaceous  matter  with  strong  perman- 
ganate, but  this  is  hardly  necessary  with  good  iron  wire  as  the  error  is  not 
more  than  2  parts  in  one  thousand  and  this  is  far  less  than  the  error  in- 
volved in  the  determination  of  small  quantities  of  phosphorus. 

2  If  there  is   considerable   residue   at  this   point  the   solution  must  be 
filtered. 


108  CHEMICAL  ANALYSIS  OF  METALS 

with  molybdenum  the  brown  sulfide  will  not  form  until  enough 
acid  ammonium  sulfate  solution  has  been  added  to  make  the 
test  acid. 

Dissolve  any  of  the  precipitate  remaining  in  the  flask  by  means 
of  5  c.c.  of  strong  ammonia  diluted  with  20  c.c.  of  water,  and  pour 
this  through  the  filter.  Wash  out  the  flask  and  the  filter  until 
the  volume  of  the  solution  amounts  to  60  or  75  c.c.  Add  10  c.c.  of 
concentrated  sulfuric  acid  and  pass  through  the  Jones  reductor. 
The  solution  is  preceded  and  followed  by  the  same  quantities 
of  dilute  sulfuric  acid  and  water  as  in  running  a  blank  or  a  stand- 
ardization. By  adding  the  strong  sulfuric  acid  to  the  ammoniacal 
solution,  the  latter  is  heated  enough  so  that  the  molybdenum  is 
reduced  readily  by  the  amalgamated  zinc.  The  solution  as  it 
passes  through  the  reductor  should  be  bright  green  in  color. 
Titrate  with  the  standard  permanganate  solution,  avoiding  much 
shaking,  until  the  permanganate  color  persists  for  1  min.  While 
adding  the  permanganate,  the  green  color  disappears,  and  the 
solution  becomes  brown,  pinkish  yellow  and  finally  colorless 
before  the  end  point  is  reached. 

Computation.  —  The  amalgamated  zinc  reduces  the  molybdenum 
from  the  hexavalent  to  the  trivalent  condition  but  there  is  a 
slight  oxidation  by  the  air  in  the  flask.  It  is  customary,  there- 
fore, to  assumed  that  the  molybdenum  is  in  the  state  of  oxidation 
corresponding  to  Mo24O37  when  the  permanganate  titration  is 
made,  which  requires  the  equivalent  of  35  atoms  of  0,  to  oxidize 
the  molybdenum  to  the  state  corresponding  to  24MoC>3.  We 
have,  then,  IP  =  12  Mo03  =  35H 

p 

1  c.c.  of  NK.MnO4  solution  =  QK  nnn  =  0.0008857  g.  P 


If  1  c.c  of  KMn04  solution  will  oxidize  a  g.  of  iron  or  b  g.  of 
pure  sodium  oxalate,  then 

P  2P 

1  c.c.  KMnO*  =  X  a  or  X  6  g.  P 


From  the  actual  burette  readings,  the  volume  of  permanganate 
required  for  the  blank  must  be  deducted  in  both  the  analysis  and 
in  the  standardization. 


PHOSPHORUS  109 

FERRIC  ALUM  MODIFICATION 

Proceed  exactly  as  in  the  preceding  method  up  to  the  point 
of  passing  the  sulfuric  acid  solution  through  the  reductor.  In- 
stead of  passing  the  reduced  solution  into  an  empty  flask,  place 
in  the  flask  about  50  c.c.  of  ferric  alum  solution1  and  make  sure 
that  the  tube  from  the  reductor  passes  into  the  solution.  In  all 
other  respects  the  two  methods  are  identical.  There  is  now 
no  oxidation  of  the  trivalent  molybdenum  by  air  in  the  flask 
but  it  is  converted  back  to  the  hexavalent  condition  by  means  of 
the  ferric  salt  and  an  equivalent  amount  of  the  latter  is  reduced 
to  ferrous  salt.  In  this  case,  therefore,  the  ferrous  iron  is  really 
titrated  by  the  permanganate  but  the  volume  of  reagent  required 
corresponds  to  the  amount  necessary  to  convert  Mo2Os  to  MoO3. 
The  computation  is  the  same  as  before  except  that  IP  =  36H. 

7.  DETERMINATION  OF  PHOSPHORUS  IN  MATERIALS 
INSOLUBLE  IN  NITRIC  ACID 

(Ferrosilicon,  Iron  Phosphide,  etc.,  and  Alloy  Steels) 

Materials  insoluble  in  nitric  acid  are  attacked  best  by  ignition 
with  a  mixture  of  sodium  carbonate  and  magnesia  as  described  in 
the  chapter  on  Silicon.  Ignite  from  1  to  3  g.  of  the  finely  pulver- 
ized material  with  six  to  eight  times  as  much  of  the  sodium 
carbonate-magnesia  mixture  (2:1). 

After  the  ignition,  dissolve  the  mass  in  hydrochloric  acid 
and  remove  the  silica  in  the  usual  manner.  After  volatilizing 
the  silica  as  silicon  tetrafluoride  by  treatment  with  sulfuric  and 
hydrofluoric  acids,  fuse  the  residue  with  sodium  carbonate, 
dissolve  the  product  of  the  fusion  in  hydrochloric  acid  and  ex- 
amine the  solution  for  phosphoric  acid.  Concentrate  the  filtrate 
from  the  silica  precipitation  (or  an  aliquot  part  of  it  if  much  phos- 
phorus is  present)  as  described  on  p.  97  and  determine  the  phos- 
phorus as  ammonium  phosphomolybdate. 

Carry  out  a  blank  determination  with  the  reagents  used  and 

1  Dissolve  100  g.  of  Fe2(SO4)3,  (NH4)2SO4,  24H2O  in  1  liter  of  water  and 
25  c.c.  of  concentrated  H2SO4  and  add  40  c.c.  of  sirupy  H3PO4.  The 
amount  of  ferric  alum  solution  used  should  be  sufficient  to  react  with  all 
the  reduced  molybdenum.  Blanks  should  be  run,  with  the  same  volume  of 
ferric  alum  in  the  flask. 


110  CHEMICAL  ANALYSIS  OF  METALS 

deduct  the  weight  of  ammonium  phosphomolybdate  thus  obtained 
from  that  obtained  in  the  regular  analysis. 

In  determining  the  phosphorus  content  of  ferrotitanium  and  of 
metallic  titanium,  wash  thoroughly  with  cold  water  the  product 
of  the  ignition  with  sodium  carbonate  and  magnesia,  filter  off  the 
insoluble  residue  and  fuse  it  with  sodium  carbonate  to  obtain  any 
residual  phosphorus.  Extract  this  second  melt  with  cold  water 
and  add  the  solution  to  that  previously  obtained ;  the  residue  will 
contain  all  the  titanium  as  sodium  titanate.1  Acidify  the  aque- 
ous extract  with  hydrochloric  acid,  evaporate  to  dryness  in  order 
to  remove  the  silica  and  then  determine  the  phosphorus  in  the 
filtrate  by  precipitation  with  ammonium  molybdate. 

8.  DETERMINATION  OF  PHOSPHORUS  IN  MATERIALS 
CONTAINING  ARSENIC 

(Hydrobromic  Acid  Method) 

Influence  of  Arsenic  upon  the  Precipitation  of  Phosphorus.— 

The  statements  in  the  literature  concerning  the  effect  of  arsenic 
upon  the  determination  of  phosphorus  in  iron  and  steel  are  con- 
flicting. Ledebur  states  that  an  arsenic  content  of  less  than  0.1 
per  cent  has  no  effect  upon  the  determination  but  cites  values 
which  are  20  per  cent  too  high  in  the  case  of  ingot  iron  containing 
0.37  per  cent  arsenic.  On  the  other  hand,  Frank  and  Hinrichsen2 
state  that  the  Finkener  method  for  determining  phosphorus  gives 
values  ranging  up  to  0.015  per  cent  in  excess  of  the  truth  when 
the  arsenic  content  is  about  0.05  per  cent.  Cast  iron  and  ingot 
iron  frequently  contain  this  amount  of  arsenic  so  that  it  would 
seem  advisable  to  take  the  effect  of  arsenic  into  consideration. 
To  make  sure  that  the  precipitate  of  ammonium  phosphomolyb- 
date contains  none  of  the  corresponding  arsenic  compound  the 
best  way  is  to  remove  the  arsenic  from  the  solution.  Various 
methods  of  accomplishing  this  have  been  proposed  but  the  hy- 
drobromic  acid  method  to  be  described  accomplishes  this  most 
simply  and  the  use  of  the  method  is  recommended  in  all  cases 

1  The  residue  is  not  pure  sodium  titanate  as  this  is  hydrolyzed  to  form  an 
insoluble  acid  titanate,  i.e.,  a  compound  containing  a  high  TiO2  content. 

2  Stahl  u.  Eisen,  28,  295.     See  also  CAMPBELL,  J.  Anal,  and  Appl.  Chem., 
1893,  2. 


PHOSPHORUS  111 

where  an  accurate  determination  of  phosphorus  is  desired  in  the 
possible  presence  of  arsenic. 

Principle. — If  a  solution  containing  arsenic  acid,  phosphoric 
acid  and  ferric  chloride  is  treated  with  pure  hydrobromic  acid 
(d.  1.42)  and  evaporated  on  the  steam  bath,  then,  as  Rothe 
showed,  all  of  the  arsenic  acid  is  volatilized,  probably  as  arsenic 
tribromide,  and  there  is  no  loss  of  phosphoric  acid.  Since  ferric 
bromide  does  not  interfere  with  the  precipitation  of  ammonium 
phosphomolybdate  it  is  evident  that  the  determination  of  the 
phosphorus  can  be  made  in  the  solution  freed  from  arsenic  by  any 
of  the  methods  already  described. 

Commercial  hydrobromic  acid  almost  always  contains  a  little 
phosphoric  acid  as  impurity.  If  there  is  only  little  of  it  present, 
the  simplest  way  is  to  carry  out  a  blank  phosphorus  determina- 
tion using  the  same  quantities  of  reagents  as  in  the  analysis 
proper,  and  make  a  deduction  from  the  results  obtained  in  the 
analysis.  If,  however,  there  is  much  phosphoric  acid  present 
in  the  hydrobromic  acid,  it  must  be  purified  by  distilling  it. 

Procedure. — Dissolve  5  g.  of  the  iron  or  steel  in  nitric  acid 
(d.  1.2),  and  treat  the  solution  exactly  as  described  on  p.  96. 
To  the  hydrochloric  acid  filtrate  from  the  silica  precipitate,  or 
to  an  aliquot  part  of  it  when  considerable  phosphorus  is  present, 
add  10  to  20  c.c.  of  pure  hydrobromic  acid  (d.  1.42  containing 
about  48  per  cent  HBr  by  weight)  and  evaporate  to  dryness 
on  the  steam  bath. 

The  hydrobromic  acid  should  not  be  added  to  a  very  con- 
centrated solution  of  ferric  chloride  on  account  of  the  danger  of 
loss  by  spattering. 

The  residue  obtained  after  evaporation  is  dark  red;  dissolve  it 
in  a  little  hydrochloric  acid  and  rinse  the  solution  into  a  beaker  of 
150  to  250  c.c.  capacity.  Remove  the  excess  of  free  acid  by  evapo- 
ration and  continue  the  analysis  as  on  p.  97  weighing  the  phos- 
phorus as  ammonium  phosphomolybdate. 

9.  DETERMINATION  OF  PHOSPHORUS  IN  MATERIALS 
CONTAINING  TUNGSTEN 

Principle. — Hinrichsen1  has  shown  that  when  tungsten  is  pres- 
ent and  the  determination  of  phosphorus  is  carried  out  by  the 
1  Mitt.  kgl.  Materialpriifungsamt,  28,  229  (1910). 


112  CHEMICAL  ANALYSIS  OF  METALS 

above  method,  the  ammonium  phosphomolybdate  precipitate 
contains  tungsten.  He  finds  that  if  the  precipitate  is  dissolved  in 
ammonia  and  the  ammoniacal  solution  treated  with  magnesia 
mixture  while  hot,  according  to  the  method  of  Jorgensen,1 
that  the  resulting  precipitate  does  not  contain  tungsten.  If 
the  precipitation  takes  place  in  the  cold,  however,  tungsten  is 
present  in  the  magnesium  ammonium  phosphate. 

Solutions  Required. — Magnesia  Mixture. — Jorgensen  recom- 
mends that  the  solution  be  prepared  from  50  g.  of  crystallized 
magnesium  chloride  (MgCl2-6H20)  and  150  g.  of  ammonium 
chloride  per  liter. 

Add  Ammonium  Nitrate  Solution. — Dissolve  150  g.  of  am- 
monium nitrate  in  water,  add  10  cc.  of  concentrated  nitric  acid 
and  dilute  to  1  liter. 

Procedure. — Dissolve  5  g.  of  the  sample  in  nitric  acid  (d. 
1.20),  evaporate  the  solution  to  dryness,  and  decompose  the 
nitrates  by  ignition.  Cool,  moisten  with  concentrated  hydro- 
chloric acid,  and  warm  with  the  addition  of  more  hydrochloric 
acid  until  the  iron  is  all  in  solution.  Evaporate  to  dryness  again 
and  render  the  silica  and  tungsten  insoluble  by  heating  to  135° 
until  no  more  vapors  of  hydrochloric  acid  are  evolved.  Cool,  dis- 
solve in  as  little  strong  hydrochloric  acid  as  possible  and  evapo- 
rate off  as  much  of  the  excess  acid  as  can  be  accomplished  without 
causing  the  deposition  of  solid  ferric  salt.  Allow  to  stand  some 
time  and  then  add  dilute  hydrochloric  acid  and  filter. 

Wash  the  residue  with  dilute  hydrochloric  acid  until  the  iron 
is  nearly  all  removed  and  finish  washing  with  the  acid  ammonium 
nitrate  solution;  this  serves  to  prevent  tungstic  acid  from  form- 
ing a  colloidal  solution  and  passing  through  the  filter. 

Ignite  the  residue  and  volatilize  the  silica  in  it  by  treatment 
with  sulfuric  and  hydrofluoric  acids.  Fuse  with  sodium  carbon- 
ate, extract  the  melt  with  water  and  treat  the  hot  solution  with 
magnesia  mixture  as  in  the  main  solution.  In  this  way  the  small 
amount  of  phosphoric  acid  is  recovered  that  is  deposited  with  the 
silica  and  tungstic  acid. 

The  filtrate  from  the  silica  precipitate  contains  most  of  the 
phosphorus;  it  may  also  contain  a  little  colloidal  tungstic  acid. 
Evaporate  the  solution  (in  a  150  or  250-c.c.  beaker)  as  far  as  pos- 
sible without  separation  of  solid,  and  precipitate  the  phosphoric 

1  Z.  anal.  Chem.,  45,  273  (1906). 


PHOSPHORUS  113 

acid  by  ammonium  molybdate  as  described  on  p.  97.  Filter 
and  wash  with  acid  ammonium  nitrate  solution. 

Dissolve  the  precipitate  in  a  very  little  2.5  per  cent  ammonia, 
receiving  the  filtrate  in  a  150-c.c.  beaker.  Usually  it  is  possible 
to  keep  the  volume  of  solution  down  to  20  c.c.  Cover  the 
beaker  with  a  watch-glass  and  heat  until  the  solution  begins  to 
boil.  Add  neutral  magnesia  mixture,  drop  by  drop,  as  long  as 
any  precipitate  forms  and  1  or  2  c.c.  in  excess.  A  flocculent 
precipitate  first  forms  which  soon  becomes  more  compact  and 
crystalline. 

Stir  the  solution  frequently  as  it  cools  and  allow  it  to  stand  at 
least  4  hr.  before  filtering.  Wash  the  precipitate  with  2.5  per 
cent  ammonia  (1  vol.  ammonia,  d.  0.96,  and  3  vol.  water)  and 
ignite  it  in  a  weighed  crucible. 

If  there  is  only  a  small  precipitate  of  magnesium  ammonium 
phosphate  it  is  better  to  dissolve  it  in  nitric  acid  (d.  1.2)  and 
precipitate  again  with  molybdate  solution,  adding  enough  solid 
ammonium  nitrate  so  that  the  solution  contains  25  per  cent  of  it. 
Weigh  this  precipitate  as  described  on  p.  97. 

10.  DETERMINATION  OF  PHOSPHORUS  IN  MATERIALS 
CONTAINING  VANADIUM 

(Vanadium  Steel  and  Ferro-vanadium) 

Principle. — In  precipitating  phosphoric  acid  in  the  presence  of 
vanadic  acid,  the  ammonium  phosphomolybdate  precipitate  is 
not  a  pure  yellow  but  has  an  orange-red  shade  owing  to  presence 
of  vanadium.  It  is  not  possible  to  remove  the  vanadium  by  the 
method  which  is  applicable  when  tungsten  is  present  for  the 
vanadium  follows  the  phosphorus  in  every  precipitation.  On  the 
other  hand,  the  vanadium  may  be  precipitated  quantitatively 
from  the  ammoniacal  solution  of  the  yellow  precipitate  by  the 
addition  of  ammonium  chloride.  The  phosphorus  and  molyb- 
denum remain  in  solution. 

After  the  removal  of  the  ammonium  vanadate,  the  phosphoric 
acid  may  be  determined  in  the  usual  manner. 

Procedure. — Dissolve  from  5  to  10  g.  of  the  sample  in  nitric 
acid  (d.  1.2)  and  remove  the  silicon  as  described  on  p.  96.  In 
the  filtrate  from  the  silica,  precipitate  the  phosphorus  according 


114  CHEMICAL  ANALYSIS  OF  METALS 

to  p.  97  and  filter  off  the  orange  tinted  precipitate.  Wash 
thoroughly  with  acid  ammonium  nitrate  solution,  dissolve  the 
precipitate  in  ammonia,  receiving  the  solution  in  a  150-c.c. 
beaker,  and  concentrate  the  solution  to  about  20  c.c. 

During  the  evaporation  of  the  solution,  add  a  drop  of  am- 
monia from  time  to  time;  if  the  solution  turns  yellow  the 
ammonia  should  make  it  colorless  again.1  To  the  cold,  slightly 
ammoniacal  solution  add  5  or  6  g.  of  solid  ammonium  chloride  and 
stir  vigorously  so  that  the  solution  quickly  becomes  saturated 
with  the  salt.  If  the  quantity  of  vanadium  present  is  not  too 
small,  the  solution  will  become  turbid  as  the  ammonium  chloride 
dissolves  and  a  fine,  flocculent  precipitate  of  ammonium  meta- 
vanadate  will  separate  out;  the  precipitation  is  complete  after 
about  6  hr. 

Filter  off  the  precipitate  and  wash  it  with  a  saturated  solution 
of  ammonium  chloride  (250  g.  to  the  liter)  until  a  little  of  the 
filtrate  gives  no  test  for  molybdenum. 

Slightly  acidify  the  filtrate  with  dilute  nitric  acid  and  add  a 
little  more  ammonium  molybdate.  Owing  to  the  large  amount 
of  ammonium  chloride  present,  the  ammonium  phosphomolyb- 
date  is  now  precipitated  with  an  excess  of  molybdic  acid  in  a 
finely  pulverulent  form.  Dissolve  the  precipitate  in  2.5  per  cent 
ammonia  and  precipitate  the  phosphorus  as  magnesium  ammo- 
nium phosphate  as  described  on  p.  97,  weighing  it  as  magnesium 
pyrophosphate. 

1  If,  besides  the  vanadium,  tungsten  is  also  present,  it  must  be  removed 
with  the  silica,  according  to  p.  112.  Otherwise  some  of  the  tungstic  acid 
will  remain  in  the  solution  and  cause  difficulty.  The  present  of  tungsten 
trioxide  in  the  phosphomolybdate  precipitate  is  shown  by  the  fact  that  the 
ammoniacal  solution  of  the  precipitate  is  not  colorless  but  yellowish  green. 
From  such  a  solution  the  vanadium  cannot  be  precipitated  satisfactorily 
by  means  of  ammonium  chloride. 


CHAPTER  V 

SILICON 

DETERMINATION  IN  MATERIALS  SOLUBLE  IN  ACID 
1.  Solution  of  the  Sample  in  Hydrochloric  Acid 

Principle. — On  treating  iron  and  steel  with  acid,  the  silicon 
present  as  silicide  is  changed  to  hydrated  silicon  dioxide,  com- 
monly called  silica.  It  is  possible  that  during  the  treatment 
with  acid  there  is  an  intermediate  formation  of  volatile,  easily 
decomposable  substances  such  as  SiH4  and  SiCU.  Thus  when 
iron  silicide  reacts  with  hydrochloric  acid,  the  reaction 

FeSi  +  6HC1  =  FeCl2  +  SiCl4  +  3H2 

may  take  place,  but  the  silicon  chloride,  as  fast  as  it  is  formed, 
reacts  with  the  water  present  to  form  hydrated  silicon  dioxide: 

SiCl4  +  2H2O  -  Si02  +  4HC1 

This  second  stage  of  the  reaction  takes  place  so  quickly  that 
there  is  never  any  loss  of  silicon  by  volatilization  (cf.  Test  An- 
alyses, p.  122).  The  silicon  dioxide,  to  a  considerable  extent, 
remains  dissolved  as  colloid  (sol).'  By  evaporating  the  hydro- 
chloric (or  sulfuric)  acid  solution  and  heating  the  residue  to  at 
least  135°  the  colloidal  silicic  acid  becomes  dehydrated  suffi- 
ciently to  convert  the  colloid  into  the  insoluble  form  (gel)  and 
by  washing  with  hydrochloric  acid  it  can  be  freed  from  the 
soluble  chlorides  of  the  other  metals. 

Procedure. — Weigh  out  2  to  4  g.  of  gray  cast  iron  or  silicon 
steel  (up  to  5  per  cent  Si),  or  5  to  10  g.  of  white  cast  iron,  ingot 
iron,  wrought  iron  or  ordinary  steel,  into  a  porcelain  casserole  of 
12  to  15  cm.  diameter.  Cover  the  casserole  with  a  watch-glass 
and  dissolve  the  metal  in  hydrochloric  acid,  d.  1.12,  using  10  c.c. 
of  acid  for  each  gram  of  metal. 

When  the  main  reaction  is  over,  place  the  casserole  on  the 
water  bath  and  heat  till  the  solution  of  the  material  is  com- 
plete. Then  rinse  off  the  bottom  of  the  watch-glass,  to  re- 
move any  silicon  dioxide  that  may  have  spattered  upon  it,  and 

115 


116 


CHEMICAL  ANALYSIS  OF  METALS 


evaporate  to  dryness.  Place  the  dish  containing  the  dry  resi- 
due upon  a  Finkener  tower  (Fig.  19)  and  heat  for  about  an  hour, 
until  no  more  fumes  of  hydrochloric  acid  are  evolved  and  the 
contents  of  the  dish  have  become  brown.  During  this  heating, 
the  dish  should  be  frequently  turned  to  secure  uniform  heat- 
ing of  the  residue.  Instead  of  using  the  Finkener  tower,  the 
casserole  and  its  contents  may  be  heated  for  an  hour  in  a  hot 
closet  kept  at  about  135°  or  upon  a  sand  bath. 

After  the  above  heating,  cover  the  dish 
with  a  watch-glass  and  allow  it  to  cool. 
Without  removing  the  watch-glass,  cover 
the  cool  residue  with  hydrochloric  acid 
(d.  1.12),  using  about  10  c.c.  for  each 
gram  of  original  substance,  and  heat  upon 
the  water  bath  until  the  chlorides  are 
entirely  dissolved,  from  time  to  time  stir- 
ring the  liquid  with  a  glass  rod. 

If  a  dark-brown  residue  of  ferric  oxide 
or  basic  salt  remains  undissolved  at  the 
bottom  of  the  dish,  it  is  because  the  resi- 
due was  heated  too  strongly.  In  such 
cases,  evaporate  the  solution  again  to  dry- 
ness  and,  without  further  heating,  take  up 
the  residue  in  concentrated  hydrochloric 
acid  (d.  1.2). 

Dilute  the  solution  with  about  150  c.c. 
of  water,  heat  nearly  to  boiling,  and  filter  promptly1  through  a 
9-cm.  filter.2 

If  the  original  material  contained  considerable  silicon  and 
there  is  danger  of  the  filter  becoming  clogged  or  of  the  filtrate 
running  through  turbid,  it  is  well  to  add  some  filter-paper  pulp 
before  filtering.  The  pulp  is  prepared  by  shaking  small  pieces 
of  filter  paper  with  hot  water  in  a  stoppered  Erlenmeyer  flask.3 

1  If  the  solution  stands  long  before  filtering  a  little  silica  dissolves. 

2  In  all  cases  where  the  precipitate  is  to  be  weighed,  a  filter  washed  with 
sulfuric  and  hydrofluoric  acids  must  be  used;  the  ash  of  such  a  filter  weighs 
less  than  0.1  mg. 

3  The  rate  at  which  the  solution  runs  through  the  filter  is  influenced  largely 
by  the  way  the  paper  is  folded  (cf.  RAASCHOU,  Z.  anal.  Chem.,  49,  759  (1910). 
Filters  which  lie  against  the  funnel  all  along  the  sides  often  work  badly, 


FIG.  19. 


SILICON  117 

After  all  the  liquid  has  passed  through  the  filter,  transfer  as 
much  as  possible  of  the  precipitate  to  the  filter  by  means  of  a 
stream  of  water  from  the  wash  bottle,  and  remove  the  last  traces 
of  precipitate  from  the  sides  of  the  dish  by  rubbing  with  a  piece 
of  filter  paper  which  has  been  moistened  with  alcohol.  The  paper 
may  be  rubbed  directly  with  the  finger  or  with  the  aid  of  a  glass 
rod  covered  on  the  end  with  smooth  rubber  tubing  (a  "police- 
man").1 

Wash  the  filter  and  residue  with  hot,  dilute  hydrochloric  acid 
(1:5)  until  the  filtrate  gives  no  blue  color  with  potassium  ferri- 
cyanide  solution.  While  still  moist,  place  the  filter  and  pre- 
cipitate in  a  weighed  platinum  crucible,  place  the  latter  on  its 
side  in  a  triangle  and  dry  carefully  by  a  small  flame  placed  near 
the  mouth  of  the  crucible.  When  all  the  moisture  has  been 
expelled,  transfer  the  flame  to  the  base  of  the  crucible  and  destroy 
the  paper  at  as  low  temperature  as  possible  without  allowing 
it  to  take  fire.  Finally  ignite  strongly,  using  the  blast  lamp  if 

whereas  filters  which  adhere  to  the  sides  of  the  funnel  only  near  the  top, 
with  the  rest  of  the  paper  hanging  free,  permit  the  more  rapid  passage  of  the 
solution  through  them.  For  this  reason,  it  is  well  to  make  the  second  fold 
of  the  filter  a  little  wider  than  a  right  angle.  To  prevent  the  formation  of 

a  channel  through  which  a  part  of  the  precipitate  may  

be  sucked,  it  is  well  to  tear  off  a  little  of  the  inside  edge 
as  shown  in  Fig.  20. 

To  place  the  paper  in  the  funnel,  take  hold  of  the 
funnel  with  the  left  hand,  insert  the  folded  filter  and 
hold  it  firmly  in  position  with  the  index  finger  of  the 
left  hand.  Then  fill  the  filter  with  water  by  a  stream 
from  the  wash  bottle,  stopper  the  funnel  tube  with  the 
finger,  raise  the  filter  a  little  to  allow  the  air  in  the 
funnel  tube  to  escape,  replace  the  filter  in  its  proper 
position  and  press  out  the  air  bubbles  between  the 
paper  and  the  glass  sides  of  the  funnel.  Then  allow 
the  water  to  run  through  the  funnel  and  pour  more  FIG.  20. 

water  upon  the  filter. 

In  filtering,  keep  liquid  in  the  funnel  but  do  not  allow  the  level  to  rise 
higher  than  the  top  of  the  paper. 

Under  no  circumstances  should  a  filter  be  used  that  is  large  enough  to 
completely  fill  the  funnel.  The  use  of  a  filter  extending  above  the  funnel 
is  never  permissible  in  quantitative  work. 

1  When  a  little  tungsten  is  present,  a  yellow  film  usually  adheres  very 
firmly  to  the  sides  of  the  procelain  dish.  This  may  be  removed  by  rubbing 
with  filter  paper  moistened  with  ammonia,  (cf.  Tungsten,  p,  199.) 


118  CHEMICAL  ANALYSIS  OF  METALS 

the  quantity  of  silica  is  considerable.  Cool  in  a  desiccator1  and 
weigh.  Repeat  the  ignition  and  weighing  until  a  constant  weight 
is  obtained. 

In  the  analysis  of  white  cast  iron,  wrought  iron,  steel,  etc., 
the  precipitate  of  silicon  dioxide  usually  appears  gray  colored 
on  the  filter  but  is  perfectly  white  after  being  ignited.  In  no 
case,  however,  where  accurate  results  are  desired,  should  it  be 
regarded  as  perfectly  pure  but  its  purity  must,  be  determined 
by  treatment  with  sulfuric  and  hydrofluoric  acids,  whereby 
volatile  silicon  fluoride  is  formed. 

To  this  end,  moisten  the  silicon  dioxide  in  the  platinum  cru- 
cible with  sulfuric  acid2  (1:1),  add  from  1  to  3  c.c.  of  pure  hydro- 
fluoric acid,3  and  evaporate  as  far  as  possible  on  the  water  bath. 
Place  the  crucible  on  the  Finkener  tower4  and  gradually  raise 
the  temperature  until  all  the  free  sulfuric  acid  has  been  expelled, 
then  decompose  any  sulfates  by  direct  ignition  over  the  free 
flame,  using  a  high  temperature  -at  the  last,  cool  in  a  desiccator, 
and  weigh.  The  loss  on  volatilization  represents  the  weight  of 
pure  SiO2: 

SiO'2  +  4HF  =  SiF4  +  H2O 

1  cf.  p.  82,  footnote. 

2  The  addition  of  the  sulfuric  acid  has  a  double  purpose.     On  the  one 
hand,  it  aids  the  reaction  between  silica  and  hydrofluoric  acid  by  acting  as  a 
dehydrating  agent  and  prevents  the  formation  of  fluosilicic  acid  by  the 
interaction  of  silicon  fluoride  and  water.     On  the  other  hand,  it  prevents  the 
volatilization  of  other  fluorides,  such  as  those  of  aluminium,  iron,  chromium, 
titanium  and  vanadium.     When  these  last-mentioned  elements  are  present, 
they  will  be  volatilized  to  some  extent  as  fluorides,  if  too  little  sulfuric  acid 
is  used,  and  the  silicon  result  will  be  too  high.     Sulfuric  acid  decomposes 
these  fluorides  before  their  boiling  points  are  reached  and  the  sulfates  are 
decomposed  upon  further  heating  into  oxide  and  volatile  sulfuric  anhydride, 
thus  leaving  them  in  the  same  condition  as  before  the  treatment.     The 
amount  of  sulfuric  acid  to  be  added  should  be  regulated  by  the  probable 
amounts  of  these  impurities.     When  tungstic  acid  is  present,  the  ignition 
before  and  after  treatment  with  hydrofluoric  acid  must  not  be  over  the 
blast  lamp.     Tungstic  acid  is  slightly  volatile  when  heated  with  sulfuric  acid 
in  a  platinum  crucible. 

3  The  purity  of  the  acid  should  be  tested  by  evaporating  some  of  it  to 
dryness  and  making  sure  that  there  is  no  weighable  residue  after  ignition. 

4  Instead  of  using  the  water  bath  and  Finkener  tower,  the  evaporation  of 
the  acid  may  take  place  by  suspending  the  crucible  in  a  larger  iron  crucible 
(by  inserting  platinum  wires  in  the  latter)  and  heating  over  the  free  flame. 


SILICON  119 

Usually,  in  spite  of  all  the  pains  that  may  be  taken  with  the 
analysis,  small  quantities  of  ferric  and  manganic  oxides  remain 
behind  after  the  treatment  with  hydrofluoric  acid,  and  in  the 
analysis  of  steels  containing  tungsten,  titanium,  chromium,  and 
vanadium  these  elements  are  invariably  present  in  the  residue 
to  a  greater  or  less  extent. 

In  the  determination  of  silicon  in  gray  cast  iron,  all  the  graphite 
remains  behind  with  the  silica  and  care  should  be  taken  to 
burn  it  completely  before  weighing.  It  is  almost  impossible 
to  obtain  a  silica  precipitate  so  pure  that  the  treatment  with 
hydrofluoric  acid  is  unnecessary  but  a  more  complete  removal 
of  the  iron  may  be  accomplished  if,  after  washing  with  dilute 
hydrochloric  acid  on  the  filter,  the  silica  is  washed  well  with 
alcohol  to  remove  substances  formed  by  the  decomposition 
of  carbide,  and  again  with  hydrochloric  acid  to  the  disappear- 
ance of  the  iron  test. 

Small  quantities  of  silicic  acid  remain  in  the  first  filtrate  but 
when  the  work  is  done  carefully  according  to  the  above  direc- 
tions the  silica  thus  lost  will  rarely  amount  to  more  than  a  frac- 
tion of  a  milligram  and  this  is  more  than  balanced  by  the  amount 
of  silica  that  is  obtained  from  the  reagents  and  from  the  dishes. 
In  iron  and  steel  analysis,  therefore,  it  is  unnecessary  to  evap- 
orate the  filtrate  from  the  silica  precipitate  to  recover  more 
silica,  although  this  is  usually  necessary  in  the  analysis  of 
silicates. 

The  filtrate  from  the  silica  determination,  together  with  any 
residue  from  the  treatment  with  hydrofluoric  acid,  may  be  used 
for  the  determination  of  manganese,  copper,  nickel,  chromium, 
aluminium,  etc.,  but  not  for  the  determination  of  phosphorus  or 
sulfur. 

X 
2.  MODIFIED  DROWN  METHOD 

In  this  method,  which  was  proposed  by  T.  M.  Drown1  and 
is  regarded  as  a  standard  method  in  the  United  States,  the  sample 
is  dissolved  in  a  mixture  of  nitric  and  sulfuric  acids  and  the 
solution  is  evaporated  until  copious  fumes  of  sulfuric  anhydride 
are  evolved.  The  hot,  concentrated  sulfuric  acid  acts  as  an 
efficient  dehydrating  agent  thus  making  the  silicic  acid  insoluble. 

1  J.  Inst.  Min.  Eng.,  7,  346;  Am.  Soc.  Testing  Materials,  1916,  217,  522. 


120  CHEMICAL  ANALYSIS  OF  METALS 

Solutions  Required. — Nitro-sulfuric  Acid. — Mix  1,000  c.c.  of 
concentrated  sulfuric  acid,  d.  1.84,  1,500  c.c.  of  concentrated 
nitric  acid,  d.  1.42  and  5,500  c.c.  of  water. 

Dilute  Hydrochloric  Acid. — Mix  100  c.c.  of  concentrated  hydro- 
chloric acid,  d.  1.2,  and  900  c.c.  of  distilled  water. 

Procedure. — Weigh  4.69  g.  of  steel  into  a  300-c.c.  porcelain 
casserole,  cover  the  dish  with  a  watch-glass  and  dissolve  the 
sample  in  80  c.c.  of  the  nitro-sulfuric  acid.  Heat  until  the  steel 
is  all  dissolved,  then  remove  the  cover  glass  and  evaporate  slowly 
until  copious  fumes  of  sulfuric  acid  are  evolved.  During  this 
evaporation  the  dish  should  not  be  covered  even  with  a  raised 
watch-glass  because  if  water  condenses  on  the  watch-glass  and 
drops  down  into  tihe  hot  sulfuric  acid  it  will  cause  spattering. 
Cool,  add  125  c.c.  of  distilled  water  and  heat  with  frequent 
stirring  until  all  the  salts  are  dissolved.  Then  add  5  c.c.  of 
concentrated  hydrochloric  acid,  heat  2  min.  and  filter  on  a  9-cm. 
filter.  Wash  the  precipitate  with  hot,  dilute  hydrochloric  acid 
till  free  from  iron  and  then  with  hot  water  until  free  from  acid. 
Ignite  the  precipitate  and  filter  in  a  weighed  platinum  crucible 
and  correct  for  impurities  obtained  after  hydrofluoric  acid  treat- 
ment exactly  as  described  in  Method  1. 

A  blank  determination  should  be  made  by  carrying  out  the 
entire  process  exactly  as  described  but  with  no  steel  in  the 
casserole.  The  weight  obtained  in  this  blank  determination 
should  be  deducted  from  the  weight  obtained  in  the  analysis. 
The  filtration  and  weighing  of  the  filter  must  be  carried  out  in 
this  blank  determination  whether  there  is  any  visible  precipitate 
or  not.  The  silica  obtained  in  the  blank  determination  comes  in 
part  from  the  action  of  the  acids  on  the  porcelain  dish  but  some 
always  come  from  the  action  of  the  acids  on  the  glass  bottles 
in  which  they  are  kept. 

By  using  the  ten-fold  factor  weight,  4.69  g.,  the  per- 
centage of  silicon  is  obtained  by  taking  the  weight  of  silicon 
dioxide  in  grams  and  moving  the  decimal  point  one  place  to  the 
right. 

Procedure  for  Cast  Irons. — Use  1.17  g.  of  sample  and  35  c.c. 
of  the  nitro-sulfuric  acid.  Otherwise,  proceed  exactly  as  in  the 
analysis  of  steel.  In  this  case,  multiply  the  weight  of  silica  in 
grams  by  40  to  get  the  per  cent  of  silicon. 


SILICON  121 

The  American  Society  for  Testing  Materials  also  suggests  a 
method  for  the  analysis  of  steels  which  is  practically  the  same 
except  that  the  steel  is  dissolved  directly  in  15  c.c.  of  concen- 
trated sulfuric  acid  and  four  times  as  much  water,  using  a  sample 
weighing  2.35  g. 

A, 
3.   NITRIC  ACID  METHOD 

Weigh  out  the  same  amount  of  metal  as  stated  for  Method 
1  and  add  12  c.c.  of  nitric  acid  (d.  1.18)  for  each  gram  of  metal. 
Add  the  acid  in  small  portions,  waiting  each  time  till  the  violent 
reaction  is  over.  When  all  the  acid  has  been  added,  heat  on 
a  water  bath  until  the  sample  has  all  dissolved.  If  there  is 
turbidity  due  to  a  brown  deposit,  bring  this  into  solution  by 
adding  more  nitric  acid  and  heating  until  eventually  a  fairly 
clear,  more  or  less  dark  brown  colored  solution  is  obtained.  Re- 
move the  watch-glass  and  evaporate  on  the  water  bath  as  near 
to  dry  ness  as  possible.  Since  a  film  forms  on  the  surface  of  the 
liquid  which  makes  it  difficult  to  evaporate  to  dryness,  rotate 
the  solution  about  the  dish  from  time  to  time  so  that  liquid 
collects  on  top  of  the  dry  layer. 

It  is  not  advisable  to  hasten  the  evaporation  by  constantly 
stirring  with  a  glass  rod  because,  during  the  subsequent  heating, 
pieces  of  the  glass  are  likely  to  splinter  off  from  the  rod  and 
render  the  determination  of  the  silicon  inaccurate. 

To  remove  all  the  nitric  acid,  heat  the  dish  upon  the  Fink- 
ener  tower  or  on  a  sand  bath.  Another  way  is  to  heat  the  dish 
on  a  piece  of  asbestos  plate,  3  mm.  thick,  over  a  Fletcher  burner, 
taking  care  to  heat  gently  at  first. 

Care  must  be  taken  to  avoid  loss  by  spattering.  When  no 
more  bubbles  of  gas  are  evolved,  remove  the  cover  glass  and 
heat  the  contents  of  the  dish  still  hotter  until  the  nitrates  are 
decomposed  (in  using  the  Finkener  tower,  remove  the  wire 
gauze).  Finally,  cover  the  dish  with  a  watch-glass  and  ignite 
over  a  free  flame  until  no  more  red  vapors  are  evolved,  showing 
that  the  decomposition  of  the  nitrates  is  complete.  The  oxides 
are  now  dark  brown  and  do  not  adhere  very  firmly  to  the  sides 
of  the  casserole. 

Allow  to  cool,  moisten  with  a  little  concentrated  hydrochloric 


122  CHEMICAL  ANALYSIS  OF  METALS 

acid  (d.  1.19)  and  warm  for  a  short  time.  Then  add  10  c.c. 
of  hydrochloric  acid  (d.  1.12)  for  each  gram  of  metal  and 
heat,  while  stirring  with  a  glass  rod,  until  all  the  ferric  oxide 
dissolves. 

To  make  sure  that  the  silicon  dioxide  is  all  in  the  insoluble 
condition,  evaporate  the  hydrochloric  acid  solution  to  dryness 
and  heat  for  some  time  at  135°.  After  cooling,  moisten  the 
residue  with  concentrated  hydrochloric  acid  (d.  1.19)  and  then 
add  the  same  volume  of  hydrochloric  acid  (d.  1.12)  as  before, 
dilute,  filter  and  wash  with  dilute  hydrochloric  acid  until  the 
washings  give  no  test  for  iron  with  potassium  thiocyanate 
solution. 

With  material  free  from  graphite,  the  silicon  dioxide  is  ob- 
tained by  this  method  in  the  form  of  a  white  or  nearly  colorless 
gelatinous  precipitate;  if  tungsten  is  present  it  is  indicated  by 
its  yellow  color. 

With  materials  containing  graphite,  the  precipitate  requires 
the  same  treatment  as  is  recommended  under  Method  1.  In 
all  cases  the  treatment  with  hydrofluoric  acid  is  necessary. 

The  filtrate  from  the  silica  can  be  used  for  the  determination 
of  substances  such  as  manganese,  copper,  nickel,  aluminium, 
chromium,  phosphorus  and  iron,  but  not  for  the  determination 
of  sulfur. 

Computation.  —  If  p  =  wt.  of  SiO2,  s  =  wt.  of  substance,  then 

_.       Si  X  p  X  100       46.93p 
Per  cent  Si  =  —          .  .  --  =  - 

X  s  s 


The  computation  is  the  same  for  all  three  of  the  methods. 

Test  Analyses.  —  Experiments  with  steel  containing  0.33  per 
cent  Si,  silicon  steel  with  1.65  per  cent  Si,  chrome  steel  with 
0.20  per  cent  Si  and  chrome-tungsten  steel  with  0.23  per  cent 
Si  have  shown  that  practically  identical  values  are  obtained  with 
Methods  1  and  3  and  the  results  by  various  chemists  on  stand- 
ard steels  and  cast  irons  prepared  by  the  Bureau  of  Standards 
at  Washington,  D.  C.,  show  that  Method  2  is  capable  of  giving 
equally  exact  results.  A  high-vanadium  content  of  the  steel  does 
no  harm. 

Accuracy  of  the  Results.  —  The  chief  sources  of  error  in  the 
determination  of  silicon  are: 


SILICON  123 

1.  Silicic  acid  present  in  the  acids. 

2.  Solution  of  silica  from  the  porcelain  dish. 

3.  Solubility  of  silicon  dioxide  in  hydrochloric  acid  solutions 
containing  ferric  chloride. 

4.  Presence  of  non-volatile  material  (oxides  of  iron,  aluminium 
or  of  the  alkalies)  in  the  hydrofluoric  acid. 

The  first  two  sources  of  error  tend  to  cause  the  results  to 
come  out  too  high  and  the  last  two  sources  tend  to  give  too  low 
results.  The  errors,  therefore,  may  compensate  one  another. 

The  extent  of  error  arising  from  the  first  and  second  sources 
should  be  determined  by  blank  tests  carried  out  with  the  same 
amount  of  acid  as  in  the  analysis.  The  quantity  of  silica  thus 
found  should  be  deducted  from  that  obtained  in  the  analysis. 
The  silicic  acid  content  of  acids  increases  slowly  up  to  a  certain 
point  upon  standing  in  glass  bottles.  The  silica  obtained  by 
evaporation  in  porcelain  dishes  is  usually  a  very  small  quantity. 

The  hydrofluoric  acid  should  be  tested  to  see  if  the  quantity 
used  in  the  analysis  leaves  a  weighable  residue.  This  is  not 
usually  the  case  with  the  best  grades  of  hydrofluoric  acid. 

As  regards  the  solubility  of  silicon  dioxide  in  hydrochloric  acid 
solutions  containing  iron,  there  are  very  few  statements  in  the 
literature.  It  is  pretty  certain,  however,  that  this  error  is  not 
large  and  probably  does  not  exceed  the  error  in  weighing.  There 
is  always  a  tendency  for  the  deposited  gelatinous  silicic  acid  to 
pass  into  the  colloidal  condition  and  this  tendency  becomes 
noticeable  if  the  solution  is  allowed  to  stand  some  time  before 
filtering. 

It  is  probably  safe  to  assume,  however,  that  the  error  in  a 
silicon  determination  when  carefully  carried  out  is  not  greater 
than  ±1  mg.  and  on  a  1-g.  sample  this  would  amount  to  0.05 
per  cent  or  on  a  10-g.  sample  to  0.005  per  cent.  It  follows,  there- 
fore, that  the  results  should  not  be  regarded  as  accurate  beyond 
the  second  decimal  and  a  silicon  content  below  0.01  per  cent 
cannot  be  determined  with  accuracy  by  any  one  of  the  above 
methods. 

Permissible  Deviation  of  Silicon  Values. — Corresponding  to 
the  sources  of  error  and  the  accuracy  attainable  in  the  deter- 
mination, the  following  table  represents  the  allowable  deviation 
in  duplicate  results  on  the  same  sample. 


124  CHEMICAL  ANALYSIS  OF  METALS 

•    Si  CONTENT  ALLOWABLE  EBKOB 

0 . 01  to    0 . 25  per  cent 0 . 005  per  cent 

0 . 25  to    1 . 00  per  cent 0.01    per  cent 

1.00  to    5. 00  per  cent 0.02    percent 

5.00  to  10.00  per  cent 0.03    per  cent 

Applicability  of  Methods  1,  2,  and  3. — All  grades  of  iron  and 
steel  that  are  soluble  in  hydrochloric  acid  or  nitric  acid  and  most 
other  metals  or  alloys  that  are  soluble  in  these  acids  (e.g.,  nickel, 
chromium,  manganese,  aluminium,  zinc,  molybdenum)  may  be 
analyzed  for  silicon  by  any  of  the  above  methods. 

Irons  containing  up  to  5  per  cent  silicon  can  be  dissolved  with- 
out much  difficulty  but  incomplete  solution  always  results  when 
the  silicon  content  is  much  higher;  in  such  cases,  therefore,  these 
methods  have  no  advantages  over  the  fusion  method  described 
under  4. 

4.  DETERMINATION  OF  SILICON  IN  MATERIALS  INSOLUBLE  IN 

ACID 

Principle. — Finely  pulverized  metals  and  alloys  can  be  attacked 
by  heating  with  a  mixture  of  pure  sodium  carbonate  and  pure 
magnesium  oxide. 

The  chemical  reaction  that  takes  place  is,1  in  the  first  place, 
an  oxidation,  and  depends  upon  the  tendency  of  sodium  car- 
bonate to  decompose  into  sodium  oxide  and  carbon  dioxide; 
the  latter  acts  upon  the  metals  forming  metal  oxide  and  car- 
bon monoxide.2  Similarly,  the  reaction  that  takes  place  with 
the  metalloid  silicon  may  be  expressed  as  follows : 

(a)  Na2C03^Na2O  +  CO2 
(6)  Si  +  2CO2  =  SiO2  +  2CO 
(c)  SiO2  +  Na20  =  Na2Si03 

The  addition  of  magnesium  oxide  prevents  the  mass  from  fusing 
and  as  a  result  the  carbon  monoxide  passes  off  more  readily  and 
without  the  danger  of  loss  by  spattering  that  would  result  if 
the  flux  were  liquid. 

1  Sodium  carbonate  alone  may  be  used  in  some  cases  but  the  metal  is 
attacked  less  readily  and  there  is  more  danger  of  loss  by  spattering. 

2  DEISS,  Ckem.-Ztg.,  34,  781  (1910). 


SILICON  125 

After  ignition,  the  mass  is  dissolved  in  water  and  dilute  acid 
and  the  silica  is  determined  as  already  described. 

Ignition  Mixtures. — It  is  well  to  have  two  mixtures  ^at  hand, 
one  consisting  of  two  parts  sodium  carbonate  to  one  part  mag- 
nesium oxide,  the  other  of  one  part  sodium  carbonate  and  two 
parts  magnesium  oxide.  The  mixtures  should  be  thoroughly 
incorporated  by  rubbing  in  a  mortar.  The  first  mixture  was 
proposed  by  Rothe1  and  the  second  by  Eschka.2  As  a  rule  the 
Rothe  mixture  is  used  but,  when  fusion  results  with  it,  the 
Eschka  mixture  is  required. 

Procedure. — The  chief  requirement  for  the  success  of  the 
ignition  process  is  that  the  material  shall  be  in  the  form  of 
very  fine  powder.  The  finer  the  powder,  the  more  rapid  and 
the  more  complete  the  attack.  Coarse  pieces  may  be  broken 
up  in  a  diamond  mortar  and  then,  if  possible,  ground  in  an  agate 
mortar  until  all  the  powder  passes  through  a  120-mesh  sieve. 

Of  material  rich  in  silicon  (metallic  silicon,  ferro-silicon)  take 
from  0.3  to  1  g.,  but  of  alloys  with  low  silicon  content  (ferro- 
chrome,  ferro-tungsten,  etc.)  take  up  to  5  g.  For  the  ignition, 
a  spacious  platinum  crucible  is  required  and  it  should  be  thor- 
oughly cleaned  by  fusing  sodium  carbonate  in  it  and  washing 
with  water  and  dilute  acid.  Before  introducing  the  sample, 
cover  the  bottom  of  the  clean  crucible  with  a  layer  3  to  4  mm. 
deep  of  the  sodium  carbonate  and  magnesia  mixture.  Mix  the 
weighed  sample  in  a  clean  agate  mortar  with  seven  to  eight  times 
as  much  of  the  ignition  mixture  and  then  carefully  transfer 
the  powder  to  the  crucible  (using  glazed  paper  beneath  the 
crucible  to  catch  any  powder  that  is  spilt).  Clean  the  mortar 
and  pestle  by  rubbing  with  a  little  more  of  the  ignition  mixture, 
and  add  the  latter  to  the  contents  of  the  crucible.  Then  place 
the  cover  on  the  crucible  and  heat  strongly  for  half  an  hour  using 
a  good  burner,  and  finally  heat  %  to  1  hr.  over  the  blast  lamp. 
Or,  if  an  electric  muffle  furnace  is  at  hand,  it  may  be  used  to 
advantage.  In  this  case  the  crucible  should  not  come  into  direct 
contact  with  the  glowing  walls  of  the  muffle  as  there  is  danger  of 
both  crucible  and  muffle  being  injured;  the  crucible  should  be 
placed  upon  a  platinum  triangle,  with  the  three  ends  of  the  latter 

1  Mitt.  kgl.  Materialpriifungsamt,  25,  51  (1907). 

2  Z.  anal  chem.,  13,  344  (1874). 


126  CHEMICAL  ANALYSIS  OF  METALS 

bent  vertically  downward  and  resting  on  the  bottom  of  the 
muffle  (cf.  Fig.  23,  p.  177). 

When  the  ignition  is  accomplished,  remove  the  crucible  and 
allow  it  to  cool.  The  cake  within  the  crucible  should  be  sin- 
tered into  a  coherent  mass  without  being  at  any  place  fused  to 
the  sides  of  the  crucible.  By  simply  inverting  the  crucible  the 
cake  should  fall  out,  leaving  the  crucible  nearly  clean.  The 
crucible  is  not  attacked  appreciably  and  experiments  have 
shown  that  after  igniting  several  grams  of  different  alloys  there 
is  no  sensible  loss  in  weight  of  the  crucible. 

Soften  the  mass  in  a  porcelain  casserole  by  treatment  with 
water;  wash  out  the  crucible  well  and  dissolve  any  adhering 
solid  by  heating  with  dilute  hydrochloric  acid,  adding  the  solu- 
tion to  the  contents  of  the  porcelain  dish.  Cover  the  dish  with 
a  watch-glass,  add  hydrochloric  acid  until  the  sodium  carbonate 
is  all  decomposed  and  heat  on  the  water  bath  until  all  the  mag- 
nesia, iron  oxide,  etc.,  is  dissolved.  For  10  g.  of  the  ignition 
mixture,  about  45  c.c.  of  hydrochloric  acid  (d.  1.12)  are 
required.  Evaporate  the  solution  on  the  bath  as  far  as  possible 
and  complete  the  necessary  dehydration  of  the  silicic  acid  by  the 
customary  heating  to  135°. l  After  cooling,  moisten  with  con- 
centrated hydrochloric  acid  (d.  1.19),  add  the  usual  quantity 
of  hydrochloric  acid  (d.  1.12)  and  heat  until  all  the  soluble 
salts  have  dissolved. 

Dilute  the  solution  with  water,  filter  off  the  silica,  wash  with 
dilute  hydrochloric  acid  and  test  the  filtrate  for  silica  by  evapo- 
rating again  to  dryness,  repeating  the  treatment  of  the  residue 
as  above,  and  filtering  through  a  fresh  filter. 

If  the  precipitated  silicon  dioxide  should  be  contaminated 
with  heavy  dark  particles  of  unattacked  material  (distinguish- 
able from  any  graphitic  particles  by  the  gritty  feeling  under  a 
stirring-rod)  then  the  precipitate,  after  being  washed  well,  must 
be  ignited  and  fused  with  sodium  carbonate  in  a  platinum  cru- 
cible. From  this  fusion,  the  silica  is  recovered  in  the  same  man- 

1  On  account  of  the  presence  of  magnesium  chloride,  the  evaporation  to 
dryness  requires  more  time  than  usual  and  in  the  subsequent  heating  of  the 
moist  residue  special  care  must  be  taken  to  avoid  loss  by  spattering.  The 
residue  must  not  be  heated  above  135°  as  the  magnesium  chloride  forms  a 
basic  salt  which  combines  to  some  extent  with  silica  if  heated  too  much. 


SILICON  127 

ner  as  described  above  for  the  treatment  of  the  mass  after  the 
original  ignition. 

After  igniting  the  silica  to  constant  weight,  determine  its 
purity  by  treatment  with  sulfuric  and  hydrofluoric  acids. 

Applicability  of  the  Ignition  Method. — The  method  is  suitable 
for  the  determination  of  silicon  in  metals  and  alloys  which  are 
insoluble  or  difficultly  soluble  in  acids,  provided  it  is  possible 
to  get  them  in  finely  powdered  form.  The  method  has  to  be 
modified  for  the  analysis  of  titanium  alloys,  inasmuch  as  solu- 
tions containing  titanium  are  likely  to  yield  silica  precipitates 
containing  a  large  part  of  the  titanium  in  the  form  of  hydrated 
titanium  dioxide. 

Modification  of  the  Silicon  Determination  for  Titanium 
Alloys. — Decompose  the  titanium-silicon  alloy  with  the  Rothe  or 
Eschka  mixture  in  the  usual  manner  and  soften  the  ignited  mass 
with  cold  water;  triturate  the  sintered  lumps  in  an  agate  mortar 
and  rinse  everything  into  a  beaker.  Carefully  avoiding  any 
heating  of  the  solution,  add  hydrochloric  acid  (d.  1.12)  until 
the  liquid  is  strongly  acid.  Allow  the  contents  of  the  beaker 
to  stand  for  an  hour  or  two  in  the  cold.  Then  heat  slowly  on 
che  water  bath,  with  frequent  stirring,  until  a  clear  solution  is  ob- 
tained in  the  course  of  a  few  hours.  Add  20  c.c.  of  sulfuric  acid 
(1  :1)  and  evaporate  until  all  the  hydrochloric  acid  is  expelled. 
Transfer  the  contents  of  the  beaker  to  a  platinum  dish  and  heat 
on  the  Finkener  tower  until  white  fumes  of  sulfuric  anhydride 
are  evolved.  As  soon  as  this  is  accomplished,  stop  heating  and 
allow  the  dish  to  cool.  Add  water  to  the  residue,  filter  off  the 
silica  and  wash  it  free  from  iron  with  dilute  hydrochloric  acid. 
Ignite,  weigh  and  treat  with  sulfuric  and  hydrofluoric  acids  as 
usual. 

Test  Analyses. — In  the  analysis  of  metallic  titanium,  dupli- 
cate determinations  on  1-g.  samples  gave  4.79  per  cent  and 
4.69  per  cent  Si.  In  the  analysis  of  ferro-titanium,  0.85  and 
0.51  g.  of  material  were  taken  for  analysis  and  the  results  obtained 
were  3.65  per  cent  and  3.60  per  cent  Si. 


CHAPTER  VI 
SULFUR 

Sulfur,  to  some  extent,  occurs  in  all  kinds  of  iron  and  steel  but 
the  maximum  quantity  ever  found  is  only  a  few  tenths  of  1  per 
cent.  It  is  always  present  in  the  form  of  sulfides,  chiefly  of  iron 
and  manganese,  and  such  sulfur  can  be  evolved  as  hydrogen  sul- 
fide  by  treatment  with  hydrochloric  acid.  Since  sulfur  tends 
toward  segregation,  care  should  be  taken  to  procure  a  good  aver- 
age sample  and  to  use  a  fairly  large  amount  of  material  for  the 
analysis. 

The  gravimetric  methods  usually  depend  upon  the  oxidation  of 
the  sulfur  to  the  sulfate  condition  and  its  precipitation  as  barium 
sulf ate.  Morrell, l  however,  weighs  the  sulfur  as  cadmium  sulfide 
and  Berzelius  obtained  a  precipitate  of  silver  sulfide,  dissolved  it 
in  nitric  acid  and  weighed  the  silver  as  chloride.  The  problem  of 
determining  sulfur  in  the  presence  of  iron  has  received  a  great  deal 
of  attention  in  the  literature.  Kiister  and  Thiel2  have  shown  that 
enormous  errors,  sometimes  amounting  to  a  loss  of  one-tenth  the 
entire  sulfur  content,  result  from  the  addition  of  barium  chloride 
to  a  boiling  solution  containing  sulfuric  acid  in  the  presence  of 
ferric  chloride.  The  loss  is  due  probably  in  part  to  the  formation 
of  a  complex  ion  containing  iron  and  sulfur  which  is  not  completely 
precipitated  and  partly  to  the  fact  that  ferric  sulfate,  or  any  com- 
plex containing  iron  and  sulfur,  loses  sulfur  upon  ignition.  These 
low  results,  therefore,  occur  especially  when  the  precipitate  is 
strongly  contaminated  with  iron,  as  shown  by  the  red  stain  of 
ferric  oxide  in  the  crucible  after  the  final  ignition.  Kiister  and 
Thiel  found  that  accurate  results  could  be  obtained  without  the 
removal  of  the  iron  in  three  ways:  (1)  by  precipitating  with 
ammonia  without  filtering,  heating  nearly  to  boiling,  adding  the 
barium  chloride  slowly,  and  finally  dissolving  the  ferric  hy- 
droxide in  dilute  hydrochloric  acid;  (2)  by  precipitating  with 
barium  chloride  in  a  cold  solution;  (3)  by  adding  the  cold  ferric 

lChem.  News,  28,  229. 
2  Z,  anorg.  Chem.,  22,  424, 

128 


SULFUR  129 

chloride  and  sulfuric  acid  solution  very  slowly  to  a  boiling,  dilute 
solution  of  barium  chloride.  It  is  well  to  remember,  however, 
that  the  trouble  caused  by  the  ferric  chloride  in  the  determina- 
tion of  small  quantities  of  sulfur  is  probably  greater  in  dilute  than 
in  concentrated  solutions,  as  Archbutt1  has  shown.  On  the  other 
hand,  barium  sulfate  has  a  decided  tendency  to  occlude  impuri- 
ties, and  occlusion  is  likely  to  be  greater  in  concentrated  solu- 
tions. In  determining  large  quantities  of  sulfur,  therefore,  it 
is  best  to  work  in  dilute  solutions. 

To  avoid  the  harmful  effect  of  ferric  chloride  upon  the  sulfur 
determinations,  it  has  been  recommended  to  reduce  the  iron  to 
the  ferrous  condition  but  this  remedy  is  not  usually  adopted  in 
iron  and  steel  analysis.  A  more  common  expedient  is  to  deter- 
mine the  sulfur  in  a  solution  free  from  iron.  This  may  be  ac- 
complished: (1)  by  expelling  the  sulfur  as  hydrogen  sulfide  and 
oxidizing  the  absorbed  gas;  (2)  by  removing  the  ferric  chloride 
by  shaking  the  solution  with  ether;  (3)  by  precipitating  the  iron 
with  an  excess  of  ammonia  or  of  sodium  carbonate;  (4)  by  treat- 
ing the  iron  or  steel  with  acid  cupric  ammonium  chloride,  which 
dissolves  the-  iron  and  leaves  the  sulfur  in  the  residue  from 
which  it  can  be  obtained  by  an  oxidizing  solution  and  treatment 
with  barium  chloride.2 

The  volumetric  determination  of  sulfur  in  iron  and  steel  is 
usually  based  upon  the  expulsion  of  the  sulfur  as  hydrogen  sul- 
fide and  the  reaction  of  this  gas  with  iodine.  The  details  of  the 
method  vary  considerably,  especially  with  regard  to  the  prelimi- 
nary absorption  of  the  hydrogen  sulfide. 

The  best-known  colorimetric  method  is  that  of  J.  Wiborgh3 
which  depends  upon  the  evolution  of  the  sulfur  as  hydrogen  sul- 
fide, the  passage  of  the  gas  through  a  cloth  disk  which  has  been 
dipped  in  cadmium  acetate  solution,  and  the  subsequent  compari- 
son with  a  series  of  similar  disks  produced  by  the  treatment  of 
steels  with  known  sulfur  content.  This  method  is  useful  in  a 
busy  laboratory.4 

1  /.  Soc.  Chem.  Ind.,  1890,  25. 

2  MEINECKE,  Chem.  News,  59,  107;  BOUCHER,  ibid.,  74,  76;  CARNOT  and 
GOUTAL,  J.  Chem.  Soc.,  72,  II,  520. 

3  Stahl  u.  Eisen,  6,  240  (1866). 

4  cf.  TREADWELL-HALL,  "Analytical  Chemistry,"  Vol.  II. 


t 

130  CHEMICAL  ANALYSIS  OF  METALS 

1.  DETERMINATION    OF   SULFUR  IN   THE   PRESENCE    OF   IRON 

In  spite  of  the  many  objections  that  have  been  raised  to  the 
direct  determination  of  sulfur  in  the  presence  of  iron,  many  chem- 
ists still  adhere  to  the  old  method  of  dissolving  the  sample  in 
nitric  acid  or  in  aqua  regia,  evaporating  to  render  the  silica  in- 
soluble, and  precipitating  the  sulfuric  acid  from  a  concentrated 
solution  in  the  presence  of  ferric  chloride.  The  method  has  been 
used  by  the  Bureau  of  Standards,  Washington,  D.  C.  in  the 
analysis  of  standardized  specimens  of  iron  and  steel  and  the 
results  have  compared  favorably  with  those  obtained  by  other 
methods. 

Treat  5.50  g.  of  borings  with  45  c.c.  of  concentrated  nitric 
acid  and  5  c.c.  of  concentrated  hydrochloric  acid  in  a  400-c.c. 
beaker.  Add  0.5  g.  of  sodium  carbonate  and  evaporate  to 
dryness.  Bake  to  decompose  nitrates,  dissolve  the  residue  in 
30  c.c.  of  concentrated  hydrochloric  acid,  and  again  evaporate  to 
dryness  for  the  purpose  of  making  the  silica  insoluble.  Redis- 
solve  the  residue  in  30  c.c.  of  strong  hydrochloric  acid,  evaporate 
the  solution  to  sirupy  consistency,  and  add  4  c.c.  of  concentrated 
hydrochloric  acid.  When  all  the  iron  is  in  solution,  add  30  to  40 
c.c.  of  hot  water,  filter  off  the  silicious  residue  and  wash  with  hot 
water.  Avoid  letting  the  nitrate  exceed  100  c.c.  Heat  it  to 
boiling  and  precipitate  with  10  c.c.  of  10  per  cent  barium  chloride 
solution.  Allow  to  stand  24  hr.  before  filtering. 

Fuse  the  insoluble  silicious  residue  with  sodium  carbonate 
and  a  little  potassium  nitrate,  extract  the  fusion  with  hot  water, 
filter,  acidify  with  hydrochloric  acid,  and  evaporate  to  dryness. 
Moisten  the  residue  with  hydrochloric  acid,  dilute  and  filter. 
Heat  to  boiling,  precipitate  hot  with  2  c.c.  of  barium  chloride  solu- 
tion, and  allow  to  stand  over  night.  The  sulfur  obtained  from 
this  insoluble  residue  should  be  added  to  that  obtained  from 
the  main  solution. 

Evaporations  should  take  place  in  an  atmosphere  free  from 
vapors  containing  sulfur  and  the  use  of  steam  baths,  electrically 
heated  hot  plates,  or  alcohol  burners  is  to  be  preferred  to  gas 
flames.  A  careful  blank  experiment  should  be  carried  along  at 
the  same  time,  using  the  same  quantities  of  reagents  and  exactly 
the  same  operations. 


SULFUR  131 

The  precipitate  of  barium  sulfate  obtained  in  the  presence  of 
the  iron  should  be  washed  with  a  hot  solution  of  2  c.c.  concen- 
trated hydrochloric  acid  and  1  g.  of  barium  chloride  per  liter 
until  free  from  iron  and  then  with  hot  water  till  free  from  chloride. 
The  second  precipitate  may  be  washed  with  hot  water  alone. 

Since  the   weight  of  sample  recommended  is  four  times  the 

S 

value  of  the  chemical  factor  ^  ~~  it  is  evident  that  the  per- 
centage of  sulfur  in  the  sample  is  equal  to  one-fourth  of  the  weight 
of  the  barium  sulfate  precipitate  when  expressed  in  centigrams. 
The  above  method  is  suitable  for  the  analysis  of  cast  iron  as 
well  as  steel  and  is  recommended  by  the  American  Society  for 
Testing  Materials. 

2.  BAMBER  METHOD  FOR  DETERMINING  SULFUR  IN  IRON  OR 

STEEL 

This  method  is  suitable  for  the  analysis  of  cast  iron  or  steel 
and  for  any  iron  alloys  which  are  decomposed  completely  by 
treatment  with  nitric  acid.  It  has  proved  to  be  a  very  reliable 
method. 

Procedure. — Dissolve  from  3  to  5  g.  of  the  sample  in  con- 
centrated nitric  acid  (d.  1.42).  After  the  iron  has  dissolved 
completely,  add  2  g.  of  solid  potassium  nitrate  and  evaporate  to 
dryness  on  the  water  bath  in  a  platinum  dish.  Heat  the  residue 
to  redness  using  an  alcohol  flame.  After  the  ignition,  add  50  c.c. 
of  a  1  per  cent  solution  of  sodium  carbonate,  boil  for  a  few  minutes 
and  filter.  Wash  the  precipitate  thoroughly  with  hot  1  per  cent 
sodium  carbonate  solution.  Acidify  the  nitrate  with  hydro- 
chloric acid  and  evaporate  to  dryness.  Moisten  the  residue  with 
2  c.c.  of  concentrated  hydrochloric  acid  and  add  50  c.c.  of  water. 
Heat  to  boiling  and  filter.  Dilute  the  filtrate  to  100  c.c.  and  pre- 
cipitate the  filtrate  with  10  c.c.  of  2  per  cent  barium  chloride 
solution.  Ignite  and  weigh  in  the  usual  manner. 

3.  DETERMINATION  OF  SULFUR  BY  THE  ETHER  METHOD* 

Necessary  Apparatus  and  Solutions. — The  requirements  are 
the  same  as  those  specified  on  pp.  71,  72. 

!c/.  KRUG,  Stahl  u.  Eisen  25,  887  (1905). 


132  CHEMICAL  ANALYSIS  OF  METALS 

Procedure. — Weigh  5  g.  of  borings  into  a  500-c.c.  round-bot- 
tomed flask  and  add  50  c.c.  of  concentrated  nitric  acid  (  d.  1.42). 
As  a  rule  there  is  little  action  in  the  cold.  Heat  cautiously  at 
first,  holding  the  flask  with  a  clamp  and  rotating  it  over  a  small 
flame,  and  have  a  dish  of  cold  water  ready  so  that  the  flask  may  be 
placed  in  it  if  the  reaction  should  become  too  violent.  After  the 
brown  nitrous  fumes  cease  to  form,  gradually  raise  the  tempera- 
ture of  the  acid  until  it  boils.  When,  at  the  end  of  an  hour  or  so, 
the  sample  is  all  dissolved,  add  0.25  g.  of  potassium  nitrate  dis- 
solved in  a  little  water,  evaporate  to  dryness  and  heat  the  residue 
until  no  more  brown  fumes  are  evolved.  After  cooling,  dissolve 
the  residue  by  heating  it  with  50  c.c.  of  concentrated  hydrochloric 
acid  (sp.  gr.  1.2)  and  again  evaporate  to  dryness.  Redissolve  in 
hydrochloric  acid,  dilute  somewhat  and  filter  off  the  silicious 
residue.  Evaporate  the  filtrate  until  a  film  of  ferric  chloride 
forms  and  redissolve  this  film  by  a  few  drops  of  hydrochloric 
acid.  It  is  now  ready  for  treatment  with  ether. 

After  cooling  the  ferric  chloride  solution,  introduce  it  into  the 
double  separatory  funnel  shown  in  Fig.  13,  p.  71,  and  wash  out 
the  contents  of  the  dish,  or  beaker,  with  hydrochloric  acid  (d. 
1.1)  keeping  the  total  volume  of  the  solution  and  washings  below 
60  c.c.  Add  30  c.c.  of  the  mixture  of  ether  and  concentrated 
hydrochloric  acid  (cf.  p.  71)  and  100  c.c.  of  pure  ether.  Cool 
under  the  water  tap  and  shake  thoroughly.  The  upper,  olive- 
green,  ether  layer  now  contains  nearly  all  the  iron  and  the  lower, 
aqueous  layer  contains  all  the  sulfuric  acid.  Carefully  transfer 
the  lower  layer  to  the  other  separatory  funnel.  Add  to  the  ether 
solution  remaining  in  the  upper  funnel,  a  few  cubic  centimeters 
of  ether  saturated  with  dilute  hydrochloric  acid  (sp.  gr.  1.1). 
Shake,  allow  to  settle  and  add  the  lower  layer  to  the  solution  in 
the  lower  funnel.  Introduce  75  c.c.  of  pure  ether  into  this  funnel, 
shake  well  and  finally  draw  off  the  lower  layer  into  a  porcelain 
evaporating  dish;  it  contains  all  the  sulfur,  very  little  ferric 
chloride  and  some  dissolved  ether.  Evaporate  to  dryness  on  the 
water  bath,  moisten  the  residue  with  a  few  drops  of  hydrochloric 
acid,  dilute  with  a  little  water  and  filter  into  a  small  beaker. 
Heat  the  filtrate  to  boiling  and  precipitate  the  sulfuric  acid  in 
the  usual  way. 

Allow  the  beaker  to  stand  in  a  warm  place  for  several  hours, 


SULFUR  133 

then  filter,  wash,  ignite  and  weigh  as  described  under  the  previous 
method.  It  is  important  to  carry  out  simultaneously  with  the 
analysis  a  blank  experiment  with  the  same  quantities  of  reagents. 

4.  IODO METRIC  DETERMINATION  OF  SULFUR  IN  STEEL 

The  iodometric  determination  of  sulfur  in  iron  alloys  is  based 
upon  the  following  reactions: 

FeS  +  2HC1  =  FeCl2  +  H2S 
H2S  +  I2     =  2HI  +  S 

and,  when  an  excess  of  iodine  is  used, 

I2  +  2Na2S2O3  =  2NaI  +  Na2S4O6 

Usually  the  gas  which  escapes  on  dissolving  the  sample  in 
hydrochloric  acid  is  not  allowed  to  act  directly  upon  iodine  but  it 
is  first  absorbed  by  some  suitable  reagent.  Sodium  hydroxide 
or  ammoniacal  cadmium  chloride  solution  is  commonly  used  but 
many  other  absorbents  have  been  proposed.  With  sodium  hy- 
droxide, the  resulting  solution,  which  contains  the  sulfur  as 
sodium  sulfide,  is  diluted  to  about  500  c.c.  and  acidified  with 
hydrochloric  acid.  A  little  potassium  iodide  is  added  and  the 
hydrogen  sulfide  is  at  once  titrated  with  a  standard  iodine  solution, 
using  starch  as  an  indicator.  Two  objections  may  be  raised  to 
this  procedure.  First,  it  is  possible  that  some  gas  other  than 
hydrogen  sulfide  may  be  absorbed  by  the  sodium  hydroxide 
solution  and  subsequently  react  with  iodine.  Second,  there  is 
opportunity  for  a  little  hydrogen  sulfide  to  escape  when  the 
solution  is  acidified  just  before  the  titration. 

When  an  ammoniacal  solution  of  cadmium  chloride  is  used  as 
the  absorbent,  both  of  the  above  objections  may  be  overcome. 
Cadmium  sulfide  is  precipitated  in  the  liquid  absorbent,  the 
precipitate  is  removed,  treated  with  a  measured  volume  of  stand- 
ard iodine  solution,  the  solution  acidified  and  the  excess  of  iodine 
titrated  slowly  with  sodium  thiosulfate  solution. 

Apparatus  and  Solutions. — A  simple  and  suitable  evolution 
apparatus  may  be  constructed  as  follows:  Use  a  250-c.c.  round- 
bottomed  flask  as  generator.  Fit  it  with  a  double-perforated 
rubber  stopper.  Through  one  hole  in  the  stopper  introduce  a 
dropping  funnel  so  that  the.  bottom  of  the  stem  reaches  nearly  to 


134  CHEMICAL  ANALYSIS  OF  METALS 

the  bottom  of  the  flask  and  through  the  other  hole  introduce  a 
delivery  tube,  bent  twice  at  right  angles,  starting  from  just 
below  the  bottom  of  the  rubber  stopper  in  the  round-bottomed 
flask,  leading  into  a  250-c.c.  Erlenmeyer  flask,  and  reaching 
nearly  to  the  bottom  of  this  flask.  Connect  this  flask  with  a 
second  250-c.c.  Erlenmeyer  flask  by  means  of  another  tube 
bent  twice  at  right  angles.  This  tube  starts  just  below  the 
stopper  in  the  first  flask  and  extends  nearly  to  the  bottom  of  the 
second  flask.  Connect  this  flask  with  a  third  Erlenmeyer  flask 
in  the  same  way.  The  first  Erlenmeyer  serves  merely  as  a  guard 
flask  and  to  remove  most  of  the  hydrochloric  acid  that  distils 
over,  whereas  the  second  and  third  flasks  are  to  contain  liquid 
into  which  the  gas  is  to  be  led. 

Prepare  a  solution  of  sodium  thiosulfate  by  dissolving  5  g.  of 
the  crystallized  salt,  Na2S203-  5H2O,  in  each  liter  of  freshly  boiled 
and  cooled  water.  Prepare  a  solution  of  iodine  by  dissolving  2.5 
g.  of  iodine  in  100  c.c.  of  water  containing  5  g.  of  pure  potassium 
iodide,  finally  diluting  the  solution  to  1  liter.  Both  of  these 
solutions  are  approximately  0.02-normal.  Titrate  the  two 
solutions  against  one  another  and  then  standardize  the  sodium 
thiosulfate  against  potassium  permanganate,  p.  62,  against  pure 
iodine,  p.  156,  or  against  copper,  p.  147. 

For  absorbing  the  hydrogen  sulfide,  prepare  an  ammoniacal 
solution  of  cadmium  salt  by  dissolving  120  g.  of  cadmium  chlo- 
ride in  1,500  c.c.  of  water  and  adding  600  c.c.  of  concentrated  am- 
monia (d.  0.90).  Use  10  c.c.  of  this  solution  in  each  of  the  two 
absorbing  flasks,  diluting  with  50  c.c.  of  water.  If  a  white  pre- 
cipitate of  cadmium  hydroxide  appears  upon  dilution,  dissolve  it 
by  the  addition  of  a  little  ammonia.  Place  25  c.c.  of  water  in  the 
first  Erlenmeyer  flask.  This  serves  to  catch  most  of  the  hydro- 
chloric acid  that  distils  over,  but  it  does  not  absorb  an  appreciable 
amount  of  sulfur  as  it  is  heated  nearly  to  boiling  toward  the  last. 

Procedure. — Weigh  5  g.  of  steel  into  the  generating  flask, 
make  sure  that  all  the  connections  are  tight  and  then  add  60  c.c. 
of  strong  hydrochloric  acid  (d.  1.19)  through  the  funnel.1  As 
soon  as  the  action  of  the  acid  on  the  metal  begins  to  slacken, 
gradually  apply  heat,  and  finally,  when  all  the  metal  is  dissolved, 

1  If  dilute  hydrochloric  acid  is  used,  lower  results  are  obtained,  cf.  pp. 
135,  138. 


SULFUR  135 

boil  the  solution  gently  until  steam  condenses  in  the  guard  flask. 
Disconnect  the  apparatus,  first  opening  the  stopper  of  the  drop- 
ping funnel  so  that  there  will  be  no  back  pressure  on  the  removal 
of  the  flame. 

Filter  off  the  precipitate  of  cadmium  sulfide,  which  is  usually 
all  in  the  middle  flask,  and  wash  the  flask  and  filter  twice  with 
water.  Transfer  the  filter  and  precipitate  to  a  beaker,  pour  over 
it  300  c.c.  of  water,  add  25  c.c.  of  the  standard  iodine  solution,  stir 
thoroughly  and  then  add  5  c.c.  of  concentrated  hydrochloric 
acid.  Dissolve  any  sulfide  precipitate  remaining  in  the  flask, 
or  in  the  glass  tubing,  by  means  of  a  little  of  this  solution,  washing 
it  all  back  into  the  beaker.  Titrate  the  excess  of  iodine  with  the 
standard  sodium  thiosulfate  solution. 

Computation.  —  If  s  represents  the  weight  of  the  steel,  n  the 
cubic  centimeters  of  thiosulfate  used,  T  the  value  of  25  c.c.  of 
iodine  solution  in  terms  of  the  thiosulfate  solution,  and  N  the 
relation  of  the  thiosulfate  to  the  normal  solution,  then 


Per  cent  S  = 


6.  DETERMINATION  OF  SULFUR  BY  THE  SIMPLIFIED  EVOLUTION 

METHOD 

For  the  routine  analysis  of  steel  the  American  Society  for 
Testing  Materials  recommends  a  method  similar  to  that  last 
described  but  with  much  simpler  apparatus.  The  method  is 
not  recommended  for  the  analysis  of  cast  irons  nor  considered 
reliable  for  all  kinds  of  steel,  some  of  which  contain  a  little  sulfur 
which  is  not  easily  converted  into  hydrogen  sulfide  on  treating 
the  sample  with  hydrochloric  acid. 

T.  G.  Elliot,  however,  finds  that  annealing  the  sample  with  a 
little  potassium  ferrodyanide  (yellow  prussiate  of  potash)  makes 
it  possible  to  get  all  the  sulfur  into  the  desired  condition.  The 
annealing  is  accomplished  by  mixing  a  5-g.  sample  of  the  metal 
with  0.25  g.  of  anhydrous  ferrocyanide  and  heating  in  a  covered 
porcelain  crucible  for  20  min.  at  750  to  850°  after  which  the 
sample  is  allowed  to  cool  slowly  and  is  broken  up  in  a  mortar. 

The  concentrations  of  the  hydrochloric  acid  and  ammoniacal 
cadmium  chloride  solution  are  different  from  those  recommended 


136 


CHEMICAL  ANALYSIS  OF  METALS 


in  Method  3  and  instead  of  oxidizing  the  hydrogen  sulfide  with 
pure  iodine  solution,  it  is  accomplished  by  means  of  potassium 
iodate  and  iodide.  The  reactions  involved  in  the  titration  are 
as  follows: 

KIO3  +  KI  +  6HC1  =  6KC1  +  3I2  +  3H2O 
I2  +  H2S  ->  2HI  +  S 

The  iodine  color  is  not  permanent  until  all  the  H2S  is  oxidized. 
Solutions    Required. — Hydrochloric    Acid    Approximately    6- 
normal. — Dilute  hydrochloric  acid,  d.  1.2  with  an  equal  volume 
of  water. 

Ammoniacal  Cadmium  Chloride. — Dissolve  10  g.  of  cadmium 
chloride  in  400  c.c.  of  distilled  water  and  add  600  c.c.  of  concen- 
trated ammonium  hydroxide  (d.  0.90). 

Potassium  Iodate. — Dissolve  1.116  g.  of  potassium  iodate 
(weighed  accurately)  and  12  g.  of  potassium  iodide  (weighed 
roughly)  in  1,000  c.c.  of  water.  One  cubic  centimeter  of  the 
solution  =  0.0005  g.  sulfur  or  0.01  per  cent  when  a  5-g.  sample 
of  steel  is  used.  The  sulfur  value  should  be  checked  by  ana- 
lyzing a  steel  of  known  sulfur 
content  by  the  method. 
Bureau  of  Standards  Stand- 
ard Steel  No.  8a  is  recom- 
mended for  this  purpose. 

Starch— Triturate  6  g.  of 
soluble  starch  with  cold  water, 
into  a  thin  paste  and  rinse 
this  into  1,000  c.c.  of  boiling 
water.  Add  a  solution  of  6  g. 
zinc  chloride  in  50  c.c.  of  water 
and  mix  well:  with  this  addi- 
FIG.  21.  tion  the  starch  solution  keeps 

better  than  in  pure  water. 

Procedure. — Weigh  5  g.  of  steel  into  the  500-c.c.  flask  shown  in 
Fig.  21.  Make  the  connections  as  shown  in  the  drawing  and 
place  10  c.c.  of  ammoniacal  cadmium  chloride  solution  mixed 
with  150  c.c.  of  distilled  water  in  the  glass  tumbler.  Add  80 
c.c.  of  6-normal  hydrochloric  acid  through  the  thistle  tube, 
gently  heat  the  contents  of  the  flask  until  all  the  steel  is  dissolved 


SULFUR 


137 


and  then  boil  the  solution  for  30  sec.  longer.  Remove  the 
tumbler,  which  will  then  contain  all  the  sulfur  as  insoluble 
cadmium  sulfide  and  add  to  it  5  c.c.  of  starch  solution  and  40 
c.c.  of  6-normal  hydrochloric  acid.  Titrate  at  once  with  the 
potassium  iodate  solution  to  the  appearance  of  a  permanent 
blue  color. 

6.  EVOLUTION  METHOD  AND  ABSORPTION  OF  HYDROGEN  SUL- 
FIDE IN  BROMINE  AND  HYDROCHLORIC  ACID 

APPARATUS  AND  SOLUTIONS  REQUIRED 

Evolution  Apparatus. — Many  forms  of  apparatus  have  been 
devised  and  that  shown  in  Fig.  22  has  proved  satisfactory.1 


FIG.  22. 

Kipp  Generator  for  producing  pure  carbon-dioxide  gas. 

Bromine  and  Hydrochloric  Acid. — Add  about  13  c.c.  of  pure 
bromine,  free  from  sulfate,  to  1  liter  of  hydrochloric  acid  (d. 
1.12),  and  mix  thoroughly  by  vigorous  shaking. 

Sodium  Chloride  Solution. — Prepare  a  10  per  cent  solution  of 
sodium  carbonate,  free  from  sulfate,  and  neutralize  with  hydro- 
chloric acid. 

Procedure. — Weigh  out,  with  an  accuracy  of  1  eg.,  about  10 
g.  of  steel  into  the  dry  flask  of  the  apparatus  shown  in  Fig.  22. 
If  the  material  is  badly  rusted,  it  is  well  to  add  1  or  2  g.  of  solid 

1  Can  be  supplied  by  Bleckmann  and  Burger  in  Berlin. 


138  CHEMICAL  ANALYSIS  OF  METALS 

stannous  chloride  to  avoid  any  oxidation  of  the  sulfur  by  ferric 
chloride. 

Fasten  the  top  on  the  apparatus,  which  has  ground-glass  con- 
nections, and  replace  the  air  in  it  by  introducing  a  stream  of  dry 
carbon  dioxide.  While  doing  this,  fill  the  ten-bulb  absorption 
tube  with  about  30  c.c.  of  the  bromine  and  hydrochloric  acid  mix- 
ture, using  enough  to  fill  all  but  the  last  three  of  the  ten  bulbs. 
Connect  the  tube  with  the  flask  and  continue  passing  the  stream 
of  carbon  dioxide  until  no  more  vapors  of  bromine  are  visible  in 
the  large  bulb  of  the  absorption  tube.  This  is  usually  accom- 
plished in  a  minute  or  two. 

Then  close  the  stopcock  just  above  the  flask,  remove  the  upper 
end  of  funnel  which  serves  for  the  introduction  of  gas,  and  add 
through  the  funnel  the  requisite  quantity  of  hydrochloric  acid. 

For  dissolving  10  g.  of  iron  it  is  best  to  use  100  c.c.  of  hydro- 
chloric acid  (d.  1.15  to  1.16).1  To  get  this  concentration  of 
acid,  fill  the  funnel  with  50  c.c.  of  concentrated  hydrochloric  acid 
(d.  1.2),  and  transfer  it  to  the  flask  with  the  aid  of  carbon  diox- 
ide pressure.  Then  add  50  c.c.  of  hydrochloric  acid  (d.  1.12),  in 
the  same  way,  avoiding  the  introduction  of  any  air  into  the  flask. 

If  the  action  of  the  acid  is  very  violent,  cool  the  flask  by  placing 
it  in  a  dish  of  cold  water;  if  it  is  slow,  heat  with  a  small  flame. 

While  the  steel  is  dissolving,  stop  passing  carbon-dioxide  gas 
through  the  apparatus,  in  order  to  avoid  driving  off  too  much 
of  the  bromine  from  the  absorption  tube.  The  solution  of  the 
sample  should  take  place  fast  enough  so  that  a  good  current  of 
gas  passes  through  the  mixture  of 'bromine  and  hydrochloric  acid. 
Gradually  increase  the  heating  of  the  flask  until  finally  the  liquid 
in  it  boils,  at  which  time  the  entire  sample  should  be  dissolved. 
The  dissolving  of  the  steel  should  not  require  more  than  an  hour 
at  the  most;  if  more  time  is  required,  as  in  the  analysis  of  some 
steels  containing  tungsten  or  molybdenum,  the  results  are  likely 
to  be  low. 

1  The  use  of  acid  which  is  more  concentrated  than  this  does  not  give 
more  accurate  results.  Fuming  hydrochloric  acid  is  not  suitable  because, 
on  heating  the  flask,  too  much  hydrochloric  acid  is  boiled  off  and  this 
causes  an  unnecessary  loss  of  bromine.  Moreover,  it  is  more  likely  to 
cause  the  liquid  to  boil  over  and  sometimes  the  evolution  of  the  gas  is  so 
uneven  that  bromine  vapors  are  sucked  back  into  the  absorption  flask, 
making  it  necessary  to  repeat  the  determination. 


SULFUR  139 

When  all  the  iron  is  dissolved,  boil  for  a  minute  more,  then  lead 
a  rapid  stream  of  carbon-dioxide  gas  through  the  apparatus,  re- 
move the  flame  from  beneath  the  flask  and  allow  the  liquid  in  it 
to  cool. 

After  10  or  15  min.,  take  off  the  absorption  tube  and  stop 
the  current  of  carbon  dioxide.  Rinse  the  contents  of  the  tube 
into  a  porcelain  dish,  add  2  or  3  c.c.  of  pure  sodium  chloride  solu- 
tion and  evaporate  to  dryness  on  the  water  bath  in  an  atmosphere 
free  from  sulfuric  acid  fumes.  Moisten  the  residue1  with  hydro- 
chloric acid,  add  a  little  water,  warm  and  filter  through  a  small 
filter  into  a  beaker  of  about  100-c.c.  capacity.  Heat  the  filtrate  to 
boiling  and  precipitate  the  sulfuric  acid  by  the  slow  addition  of  5 
c.c.  of  barium-chloride  solution  (100  g.  BaCl2  2H20  in  500  c.c. 
water).  Stir  well  and  allow  to  stand  in  a  warm  place  until  the 
barium  sulfate  has  settled  out.  Then  filter  through  a  small  ash- 
less  filter,  taking  the  precaution  to  change  the  beaker  under  the 
funnel  before  getting  the  precipitate  on  the  filter,  and  wash  first 
with  very  dilute  hydrochloric  acid  and  finally  with  hot  water  till 
free  from  chloride. 

Ignite  the  filter  and  precipitate  very  gently  until  the  ash  is 
white  and  finally  over  the  full  heat  of  the  Bunsen  burner,  with  the 
cover  of  the  crucible  off.  Do  not  heat  over  the  blast  because  of 
the  danger  of  converting  barium  sulfate  into  barium  oxide. 

On  account  of  the  possibility  of  small  quantities  of  sulfuric  acid 
being  present  in  the  reagents  and  the  danger  of  contamination 
from  the  atmosphere  (due  to  the  use  of  sulfuric  acid  or  to  the 
burning  of  illuminating  gas  in  the  laboratory)  it  is  always  desir- 
able to  carry  out  a  blank  determination  with  the  same  quantities 
of  reagents  and  the  same  operations  as  in  the  analysis.  More- 
over, the  evaporation,  precipitation,  filtration,  etc.,  should  take 
place  at  the  same  time  the  analysis  itself  is  being  made.  The 
weight  of  barium  sulfate  obtained  in  the  blank  experiment  should 
be  deducted  from  that  obtained  in  the  analysis.  Such  blank 
experiments  are  desirable  in  all  determinations  of  relatively  small 
quantities  of  substances.  When  the  substance  determined  is 

1  If  the  material  analyzed  contains  much  carbon,  the  residue  obtained  at 
this  stage  in  the  analysis  often  contains  bromine  substitution  products  of 
hydrocarbons.  These  color  the  residue  and  give  it  a  sharp  odor  but  do  not 
affect  the  analysis  in  any  way. 


140  CHEMICAL  ANALYSIS  OF  METALS 

present  in  large  quantities,  as  in  the  determination  of  sulfur  in  a 
nearly  pure  sulfate,  the  negative  errors  due  to  the  solvent  action 
of  the  reagents  upon  the  precipitate  may  more  than  compensate 
the  amount  obtained  from  the  reagents. 

The  solution  obtained  in  the  distillation  flask  after  the  sulfur 
has  been  removed  as  hydrogen  sulfide,  may  be  used  for  other  de- 
terminations. It  is  not  suitable  for  the  determination  of  silicon, 
however,  as  there  is  likelihood  of  small  particles  of  gelatinous 
silicic  acid  adhering  to  the  sides  of  the  flask  so  firmly  that  they 
cannot  be  easily  removed.  After  rendering  all  the  silicic  acid 
insoluble,  by  the  method  described  on  p.  115,  the  filtrate  may  be 
used  for  the  determination  of  copper,  manganese,  nickel,  chro- 
mium or  vanadium. 

Computation. — The  sulfur  content  of  the  steel,  when  s  repre- 
sents the  original  weight  of  the  metal  and  p  the  weight  of  the  pre- 
cipitate, is 

SXpXIOO       13.74p 

BaS04  X  s  =     —     =  Per  centS 

APPLICABILITY  OF  THE  METHODS  FOR  DETERMINING  SULFUR 
IN  IRON  AND  STEEL 

Comparative  tests  have  shown  that  the  rapid  evolution 
methods,  when  properly  carried  out,  give  accurate  results  with 
most  samples  of  steel.  The  time  required  for  carrying  out  the 
analysis  is  short  and  there  is  no  danger  of  contamination  from 
sulfur  in  the  laboratory  atmosphere.  If  the  acid  used  is  too 
dilute,  or  if  the  solution  of  the  steel  takes  place  too  slowly,  the 
results  are  likely  to  be  a  little  low.  Certain  samples  of  cast  iron 
and  some  steels  contain  sulfur  in  a  condition  such  that  it  is  not 
evolved  as  hydrogen  sulfide  upon  treatment  with  acid.  This 
difficulty  can  usually  be  overcome  by  annealing  the  sample 
before  analyzing  it  for  sulfur. 

The  Bamber  method  is  recommended  in  the  United  States  for 
settling  disputed  analyses.  The  Bureau  of  Standards,  Wash- 
ington, D.  C.,  have  had  success  with  Method  d  although  it  is 
open  to  the  theoretical  objection  that  errors  are  involved,  as 
already  pointed  out,  in  precipitating  sulfuric  acid  in  the  presence 
of  iron. 

The  first  evolution  method,  Method  a,  gives  excellent  results 
but  occasionally  they  are  too  low.  It  is  slightly  more  reliable 


SULFUR  141 

than  the  other  evolution  method  because  it  provides  for  the  oxi- 
dation of  any  gas  containing  sulfur. 

The  method  based  upon  the  removal  of  the  ferric  chloride  by 
ether  is  probably  as  reliable  as  any  method  that  has  been  proposed 
but  is  not  used  in  busy  laboratories  on  account  of  the  time  re- 
quired for  the  analysis  and  on  account  of  the  unpleasantness  and 
danger  involved  in  constantly  working  with  ether. 

Accuracy  of  the  Results. — Duplicate  determinations  should 
agree  within  0.005  per  cent  in  the  analysis  of  steels  containing 
0.2  to  0.4  per  cent  sulfur  and  within  0.003  per  cent  in  the  case  of 
steels  containing  0.015  per  cent  sulfur  or  less. 

7.  DETERMINATION     OF    SULFUR    IN    INSOLUBLE     MATERIALS 

(Ferro-silicon,  Ferro-chrome,  Etc.) 

The  mixture  of  1  part  sodium  carbonate  and  2  parts  magnesium 
oxide,  known  as  Eschka's  mixture,  is  suitable  for  determining  a 
small  sulfur  content  of  an  insoluble  substance.  The  sample 
should  be  in  the  form  of  a  fine  powder  and  particular  care  should 
be  taken  to  avoid  contamination  with  sulfur  in  the  atmosphere. 
The  use  of  the  gas  flame,  therefore,  is  prohibited.  An  alcohol 
burner  may  be  used  for  the  ignition  but  an  electric  furnace  is 
even  better.  Ignite  the  insoluble  material  in  a  platinum  dish 
with  about  eight  time  as  much  Eschka's  mixture  until  the  oxida- 
tion of  the  sample  is  complete. 

Transfer  the  ignited  mass  to  a  beaker  and  rinse  the  dish,  using 
about  50  c.c.  of  water.  Add  15  c.c.  of  saturated  bromine  water 
and  boil  5  min.  Allow  the  residue  to  settle,  decant  the  solution 
through  a  filter,  boil  a  second  and  a  third  time  with  30  c.c.  of 
water,  and  finally  wash  the  residue  with  hot  water  until  the 
filtrate  shows  no  test  for  chloride.  Add  3  c.c.  of  hydrochloric 
acid  (d.  1.1)  and  evaporate  the  solution  to  dryness  to  de- 
hydrate silica.  Take  up  the  residue  with  5  c.c.  of  hydrochloric 
acid,  dilute,  filter  and  precipitate  the  sulfuric  acid  in  the  filtrate 
with  a  hot,  dilute  solution  of  barium  chloride.  Filter,  ignite  and 
weigh  the  precipitate  of  barium  sulfate  in  the  usual  manner. 

Test  Analyses. — The  sulfur  was  determined  in  a  sample  of 
ferro-silicon  using  a  2-g.  sample  and  15  g.  of  the  Eschka  mix- 
ture. Duplicate  determinations  agreed  within  1  mg.  of  barium 
sulfate  showing  respectively  0.037  and  0.044  per  cent  S. 


CHAPTER  VII 
COPPER 

Copper,  to  the  extent  of  a  few  tenths  of  1  per  cent,  is  a  common 
constituent  of  iron  and  steel.  Often  its  presence  is  accidental 
but  in  some  cases  it  is  added  intentionally  for  the  purpose  of 
preventing  corrosion. 

1.     PRECIPITATION  AS  SULFIDE  FROM  ACID  SOLUTION 

Principle. — The  solution  containing  ferrous  chloride  and  cupric 
chloride  in  the  presence  of  free  hydrochloric  acid  is  treated  with 
hydrogen  sulfide,  which  precipitates  cupric  sulfide.  The  pre- 
cipitate is  purified  and  the  copper  determined  as  oxide. 

Procedure. — Dissolve  10  g.  of  the  iron  or  steel  in  100  c.c.  of 
hydrochloric  acid  (d.  1.12)  in  a  beaker  of  about  500-c.c.  capacity. 
Heat  on  the  water  bath  until  all  the  metal  is  dissolved. 

Instead  of  using  a  separate  sample  for  this  determination,  the 
solution  obtained  in  the  determination  of  sulfur  by  the  evolution 
method  (p.  140)  or  the  filtrate  from  the  silicon  determination  may 
be  taken. 

When  the  iron  is  all  dissolved,  dilute  the  solution  to  about 
200  c.c.1  and  introduce  hydrogen  sulfide  gas  for  %  hr.  Then 
heat  a  short  time  on  the  water  bath  to  expel  most  of  the  excess 
hydrogen  sulfide  and  filter  through  a  filter  that  runs  rapidly. 
Wash  the  precipitate  and  filter  with  water  containing  hydrogen 
sulfide  until  all  the  hydrochloric  acid  has  been  removed,  taking 
care  during  all  the  filtration  and  washing  to  keep  liquid  in  the 
filter.  This  is  important  because  copper  sulfide  oxidizes  rapidly 
to  copper  sulfate  on  standing  in  the  air  and  then  washes  through 
into  the  filtrate,  causing  a  turbidity  there.  It  is  necessary  to 
remove  all  the  hydrochloric  acid  from  the  precipitate  because 

1  If  the  solution  stands  too  long  some  of  the  iron  is  oxidized  to  the  ferric 
condition  which  causes  the  precipitation  of  sulfur  when  hydrogen  sulfide  is 
introduced. 

142 


COPPER  143 

otherwise  some  cupric  chloride  will  be  lost  by  volatilization 
during  the  next  operation. 

As  soon  as  the  washing  is  complete,  transfer  the  precipitate  to  a 
large,  unweighed  porcelain  crucible  and  smoke  off  the  filter  paper 
by  means  of  a  low  flame,  keeping  the  temperature  as  low  as  pos- 
sible. Moisten  the  ash  with  concentrated  nitric  acid  and  heat 
again  until  the  carbon  is  all  consumed.  To  the 'residue,  which 
now  contains  all  the  copper  as  black  cupric  oxide,  add  a  few 
cubic  centimeters  of  hydrochloric  acid  (d.  1.12)  and  heat  until 
all  the  copper  oxide  is  dissolved.  Evaporate  the  solution  to 
dryness,  to  render  traces  of  silica  insoluble,  treat  the  residue  with 
hydrochloric  acid,  dilute  and  filter  into  a  small  beaker  of  100  to 
150-c.c.  capacity.  Wash  the  filter  with  water  containing  a  little 
hydrochloric  acid  but  avoid  letting  the  filtrate  exceed  about 
30  c.c. 

To  precipitate  the  copper  again,  add  10  to  20  c.c.  of  saturated 
hydrogen  sulfide  water  and  heat  on  the  water  bath  with  frequent 
stirring  until  the  precipitate  collects  together  and  the  supernatant 
liquid  is  clear.  Filter  through  a  small  filter  until  all  the  hydro- 
chloric acid  is  removed,  using  wash  water  containing  hydrogen 
sulfide.  Ignite  the  precipitate  in  a  weighed  porcelain  crucible  at 
a  low  temperature  until  all  the  carbon  of  the  filter  is  consumed, 
cool  in  a  desiccator  and  weigh  as  cupric  oxide,  CuO. 

If  care  is  not  taken  in  igniting  the  copper  sulfide  precipitate, 
there  is  danger  of  mechanical  loss. 

The  ignited  and  weighed  cupric  oxide  should  dissolve  in 
hydrochloric  acid  without  leaving  a  weighable  residue;  the  addi- 
tion of  ammonia  in  excess  should  then  give  a  clear,  deep-blue 
solution. 

In  the  analysis  of  cast  iron  containing  considerable  silicon  and 
graphite,  the  silicon  should  be  removed  at  the  start  by  Method 
1,  p.  115,  and  the  copper  precipitated  as  sulfide  in  the  filtrate. 
The  residue  obtained  after  treatment  of  the  silica  with  sulfuric 
and  hydrofluoric  acids  should  also  be  examined  for  copper. 

Computation. — If  p  represents  the  weight  of  the  copper  oxide 
obtained  from  a  sample  of  metal  weighing  s  g.  then 

79.89  X  p 
per  cent  Cu  =  - 


144  CHEMICAL  ANALYSIS  OF  METALS 

2.  DETERMINATION  AFTER  REMOVAL  OF  IRON  WITH  ETHER 

Principle. — By  shaking  with  ether  a  hydrochloric  acid  solution 
containing  considerable  ferric  chloride  and  a  little  cupric  chloride, 
the  greater  part  of  the  former  salt  dissolves  in  the  ether  while  all 
of  the  latter  salt  remains  in  the  aqueous  layer. 

Procedure. — Dissolve  about  10  g.  of  the  sample  in  dilute  nitric 
acid  (d.  1.2)  and  remove  the  silicon  as  described  in  Method  1 
on  p.  1 15.  In  the  filtrate  carry  out  the  Rothe  ether  separation  as 
described  under  Manganese,  p.  73.  The  aqueous  hydrochloric 
acid  solution  then  contains  only  a  little  iron,  but  all  of  the  copper 
manganese,  nickel,  chromium,  etc.  Evaporate  the  solution  on 
the  water  bath  to  remove  dissolved  ether,  take  up  the  residue  in  a 
little  hydrochloric  acid,  add  water  and  filter  the  solution,  if  neces- 
sary, to  remove  traces  of  silica  and  titanium  oxide.  Precipitate 
the  copper  with  hydrogen  sulfide  according  to  the  procedure  given 
in  Method  1,  cautiously  ignite  the  precipitate  in  a  porcelain  cru- 
cible and  weigh  as  cupric  oxide,  CuO. 

3.  REMOVAL  OF  THE  IRON  WITH  SULFURIC  ACID1 

Principle. — In  the  potential  series  of  the  metals,  iron  has  a 
greater  and  copper  a  smaller  solution  pressure  than  hydrogen. 
For  this  reason  iron  dissolves  readily  in  dilute  sulfuric  acid  while 
copper,  in  the  absence  of  oxidizing  agent,  does  not.  To  make  sure 
that  traces  of  copper  are  not  dissolved,  hydrogen  sulfide  water 
should  be  added  to  the  solution  before  filtering. 

Solutions  Required. — Sulfuric  Acid. — Mix  200  c.c.  of  concen- 
trated sulfuric  acid,  d.  1.84,  and  800  c.c.  of  water. 

Potassium  Ferrocyanide. — Dissolve  10  g.  of  the  crystals  in  100 
c.c.  of  distilled  water. 

Standard  Copper  Nitrate. — Dissolve  2  g.  of  pure,  electrolytic 
copper  in  20  c.c.  of  nitric  acid  (1  vol.  cone,  acid  to  1  of  water) 
and  dilute  to  1,000  c.c.  Each  cubic  centimeter  of  this  solution 
contains  0.02  per  cent  Cu  on  the  basis  of  a  10-g.  sample. 

1  This  method  is  recommended  by  the  U.  S.  Bureau  of  Standards,  Circular 
No.  14  (1913).  The  directions  given  are  those  authorized  by  the  American 
Society  for  Testing  Materials. 


COPPER  145 

Procedure. — Dissolve  10  g.  of  the  sample  in  75  c.c.  of  the 
sulfuric  acid  and  then  add  150  c.c.  of  water.  Heat  the  solution 
and  saturate  with  hydrogen  sulfide.  Filter  and  wash  the  residue 
wi$i  1  per  cent  sulfuric  acid  containing  hydrogen  sulfide,  till 
free  from  iron.  Incinerate  the  paper  with  its  contents  in  a 
porcelain  crucible  and  fuse  with  0.5  g.  of  sodium  bisulfate  (or 
the  potassium  salt.  Extract  the  melt  with  hot  water,  filter  and 
complete  the  determination  electrolytically  in  sulfuric  acid  solu- 
tion as  in  Method  4  or  colorimetrically  as  follows: 

Evaporate  the  aqueous  solution  to  about  25  c.c.,  filter  into  a 
100-c.c.  Nessler  tube  and  wash  the  filter  with  hot  water. 

(a)  If  the  solution  is  a  strong  blue,  to  another  100-c.c.  Nessler 
tube  add  50  c.c.  distilled  water,  5  c.c.  of  concentrated  ammonium 
hydroxide  solution  and  the  standard  copper  solution  from  a 
burette  until  the  blue  colors  match. 

(6)  If  the  solution  is  a  faint  blue,  add  dilute  sulfuric  acid  to 
faint  acidity  and  then  a  few  drops  of  the  potassium  ferro-cyanide 
solution.  To  another  Nessler  tube  add  50  c.c.  of  distilled  water, 
a  few  drops  of  ferrocyanide  solution  and  the  copper  solution 
from  a  burette  until  the  reddish  brown  colors  match. 

4.  ELECTROLYTIC  DETERMINATION  OF  COPPER 

Principle. — The  first  copper  sulfide  precipitate  obtained  in 
Method  1  or  in  Method  2,  as  well  as  the  copper  sulfate  solution 
obtained  in  Method  3,  may  be  used  for  the  electrolytic  determina- 
tion of  copper.  The  electrolytic  deposition  of  copper  can  be  ac- 
complished successfully  under  quite  varying  conditions.  For 
this  reason  the  procedures  described  by  different  chemists  often 
vary  considerably.  It  is  well  to  bear  in  mind,  however,  that  too 
much  acid  prevents  the  deposition  and  too  strong  currents  are 
likely  to  cause  spongy  deposits.  In  general,  stronger  currents 
can  be  employed  with  a  gauze  cathode  than  when  a  plate  elec- 
trode is  used. 

Moreover,  the  more  concentrated  the  solution  and  the  larger 
the  surface  of  cathode  exposed,  the  stronger  the  current  may  be. 
Stirring,  when  accomplished  by  rotating  one  of  the  electrodes,  by 
an  electromagnetic  effect  in  Frary's  apparatus  (p.  179),  or  in  any 
other  way,  also  shortens  the  time  required  for  electrolysis  by  per- 
mitting the  use  of  stronger  currents. 
10 


146  CHEMICAL  ANALYSIS  OF  METALS 

Procedure. — In  case  the  analysis  is  started  as  described  in 
Method  1  or  in  Method  2,  dissolve  the  ignited  cupric  oxide,  ob- 
tained by  igniting  the  sulfide  precipitate,  in  a  little  nitric  acid,  add 
a  few  drops  of  sulfuric  acid  and  evaporate  until  fumes  of  sulfuric 
anhydride  are  evolved.  Cool,  add  enough  water  to  dissolve  all 
the  copper  sulfate  and  transfer  the  solution  to  a  small  beaker  of 
not  over  200-c.c.  capacity. 

Dilute  this  solution,  or  that  obtained  in  Method  3,  to  about  50 
c.c.  and  electrolyze  with  stationary  electrodes  and  a  current  of 
about  0.2  ampere  or,  if  a  gauze  cathode  and  stirring  apparatus 
are  available,  a  much  stronger  current  may  be  employed  and  the 
analysis  finished  more  quickly. 

When  all  the  copper  is  removed  from  the  solution,  which  is 
usually  the  case  at  the  end  of  3  hr.  with  stationary  electrodes, 
quickly  detach  the  cathode  and  wash  it  immediately  by  plunging 
it  into  water  in  a  beaker.  Rinse  with  alcohol,  dry  a  short  time 
at  100°,  cool  and  weigh.  Test  the  solution  for  copper  by  passing 
hydrogen  sulfide  into  it.  If  any  precipitate  of  copper  sulfide 
is  obtained,  it  may  be  filtered  off,  ignited  in  a  porcelain  crucible 
and  weighed  as  cupric  oxide,  CuO,  or  the  oxide  may  be  dis- 
solved in  acid  and  the  solution  electrolyzed  as  before,  using  a 
clean  electrode  surface. 

Accuracy  of  the  Results. — With  care,  the  copper  content  of  a 
steel  can  be  determined  by  any  one  of  the  above  methods  with 
an  error  of  not  more  than  1  mg.  in  the  final  weight.  Using 
a  10-g.  sample  this  corresponds  to  an  error  of  0.01  per  cent.  If 
the  quantity  of  copper  in  the  steel  is  less  than  0.2  per  cent 
duplicate  determinations  should  agree  within  about  0.005 
per  cent. 

5.  THE  RAPID  DETERMINATION   OF  COPPER  IN  STEEL1 

Principle. — This  procedure  is  a  modification  of  A.  H.  Low's 
method2  for  determining  copper  in  ores.  Copper  is  electro- 
negative to  aluminium  in  the  potential  series  of  metals  and  for 
this  reason  aluminium  displaces  copper  when  placed  in  the  solu- 
tion of  a  copper  salt.  Moreover,  copper  is  lower  than  hydrogen 

1  KOEPPING,  E.  D.,  /.  Ind.  Eng.  Chem.,  6,  696  (1914). 

2  Low,  A.  H.,  "Technical  Methods  of  Ore  Analysis." 


COPPER  147 

in  the  series,  so  that  hydrochloric  and  sulfuric  acids  do  not  dis- 
solve copper  in  the  absence  of  an  oxidizing  agent;  if  any  copper 
dissolves  the  aluminium  will  precipitate  it  even  in  the  presence  of 
acid.  The  residual  copper  is  dissolved  by  nitric  acid,  the  solution 
is  neutralized  by  ammonia,  acidified  with  acetic  acid  and  the 
cupric  ions  are  changed  to  cuprous  iodide  by  treatment  with 
potassium  iodide  whereby  an  equivalent  weight  of  iodine  is  set 
free: 

2Cu(C2H3O2)2  +  4X1  =  Cu2I2  +  4KC2H3O2  +  I2 

The  free  iodine  is  titrated  with  standard  sodium  thiosulfate 
solution. 

Solutions  Required. — (1)  Standard  Sodium  Thiosulfate  Solu- 
tion.— Dissolve  25  g.  of  pure,  crystallized,  sodium  thiosulfate 
Na2S203-5H20  in  water  and  dilute  the  solution  to  5  liters.  The 
solution  is  approximately  0.02-normal.  Use  water  that  has  been 
recently  boiled  free  from  carbon  dioxide  and  cooled.  Standardize 
the  solution  against  10  c.c.  of  tenth-normal  potassium  per- 
manganate solution  (p.  63),  against  about  0.1  g.  of  pure  iodine 
(p.  156),  or  against  metallic  copper. 

To  standardize  against  pure  metallic  copper,  dissolve  about  0.1 
g.  of  pure  copper,1  in  a  200-c.c.  Erlenmeyer  flask  with  5  c.c.  of  a 
mixture  of  equal  parts  nitric  acid  (d.  1.42)  and  water.  Dilute 
the  solution  to  25  c.c.  and  boil  a  few  minutes  to  remove  oxides 
of  nitrogen.  To  remove  the  last  traces  of  nitrous  acid,  add  5  c.c. 
of  bromine  water  and  boil  until  the  excess  bromine  is  expelled. 
Cool  somewhat  and  add  strong  ammonia  until  a  slight  excess  is 
present.  Boil  off  the  excess  ammonia  and  add  7  c.c.  of  strong 
acetic  acid,  which  dissolves  any  copper  oxide  that  may  have 
been  deposited  by  boiling  the  blue  ammoniacal  copper  solution. 
Cool  to  room  temperature,  add  2  g.  of  pure  potassium  iodide, 
and  titrate  with  sodium  thiosulfate  until  nearly  colorless.  Then 
add  2  c.c.  of  starch  solution  (0.5  g.  of  soluble  starch  dissolved  in 
25  c.c.  of  boiling  water;  the  starch  solution  should  cool  before 
using  it)  and  finish  the  titration. 

In  making  the  titration  for  the  first  time,  it  should  be  borne 
in  mind  that  cuprous  iodide  is  not  white. 

1  This  will  react  with  about  80  c.c.  of  the  dilute  sodium  thiosulfate 
solution. 


148  CHEMICAL  ANALYSIS  OF  METALS 

The  reactions  that  take  place  during  the  standardization  may 
be  expressed  as  follows : 

3Cu  +  8HNO3  =  3Cu(N03)2  +  4H2O  +  2NO 

NO  +  O  =  N02 

2N02  +  H20  =  HN02  +  HNO3 

HNO2  +  Br2  +  H2O  =  HNO3  +  2HBr 

Cu++  +  6NH3  =  Cu(NH3)6++ 
Cu(NH3)6++  +  6H+  =  Cu  ++  +  6NH4+ 
2  Cu++  +  41-  =  Cu2I2  +  I2 
2S2O8-  +  I2  =  S406=  +  21- 

Procedure. — Weigh  from  3  to  10  g.  of  the  metal,  according  to 
the  probable  copper  content,  into  a  small  beaker  and  dissolve  in 
35  c.c.  of  6-normal  hydrochloric  acid  (d.  1.12)  or  sulfuric  acid 
(d.  1.18).  Dilute  the  solution  with  35  c.c.  of  water  and  in- 
troduce a  strip  of  aluminium  foil,  bent  so  that  it  will  not  lie  flat 
on  the  bottom  of  the  beaker,  and  boil  the  solution  for  20  min. 

Remove  the  beaker  from  the  hot  plate  and  wash  down  the 
cover  glass  and  sides  of  the  beaker  with  hot  water.  Filter 
through  a  11-cm.  filter  and  wash  the  residue  promptly  with 
hot  water.  Puncture  the  filter,  and  rinse  the  precipitated  copper 
into  a  30-c.c.  Erlenmeyer  flask.  Cover  the  aluminium,  in  the 
original  beaker  in  which  the  copper  was  deposited,  with  a  mix- 
ture of  3  c.c.  concentrated  nitric  acid  (d.  1.42)  and  7  c.c.  of 
water  and  pour  the  acid  through  the  pierced  filter.  Finally 
wash  the  aluminium  and  the  filter  with  hot  water.  Boil  the 
copper  nitrate  solution  a  few  minutes  to  remove  nitrous  fumes, 
cool  somewhat,  and  then  add  7  c.c.  of  strong  ammonia  (d. 
0.90).  Boil  until  the  deep  blue  solution  becomes  pale  blue  and 
the  ammonia  odor  is  faint.  Add  10  c.c.  of  80  per  cent  acetic 
acid  and  boil  1  min.  more.  Allow  the  solution  to  cool  and  when 
at  the  room  temperature,  or  colder,  add  3  gr.  of  potassium 
iodide  and  at  once  titrate  the  liberated  iodine  with  the  sodium 
thiosulfate  solution. 

Computation. — If  in  the  standardization  of  the  solution,  n\  c.c. 
of  thiosulfate  were  required  for  e\  g.  of  copper,  then 

1  c.c.  Na2S2O3  =  --  =  T  g.  copper 
n\ 


COPPER  149 

If  the  solution  was  standardized  against  10  c.c.  of  a-normal 
permanganate,  and  w2  c.c.  of  thiosulfate  were  required;  then 

10a  X  0.06357 

1  c.c.  Na2S2O3  =  —  -  =  T  g.  copper 

HZ 

If  standardized  against  pure  iodine,  and  e3  g.  of  iodine  required 
n3  c.c.  of  solution, 

e*  0.06357 
1  c.c.  Na2S203  -  —  -  ==  T  g'  copper 


If  n  c.c.  of  thiosulfate  solution  were  required  in  the  analysis  of 
s  g.  of  steel,  then 

,  ^ 
per  cent  Cu  = 


CHAPTER  VIII 
CHROMIUM 

Chromium  to  some  extent,  though  not  usually  more  than  0.1 
per  cent,  is  present  in  nearly  all  samples  of  iron  and  steel.  Special 
steels  are  prepared  by  the  addition  of  chromium,  or  chromium 
alloy,  to  steel;  in  this  way  chrome,  chrome-nickel,  silicon-chrome, 
chrome-tungsten  and  chrome-vanadium  steels  are  prepared. 
In  the  preparation  of  these  steels,  ferro-chrome  and  chrome- 
manganese  are  used  chiefly.  The  chromium  content  of  these 
two  alloys  varies  considerably. 

1.  DETERMINATION  OF  CHROMIUM  BY  THE  BARIUM  CARBONATE 

METHOD1 

Principle. — The  sample  is  dissolved  in  6-normal  hydrochloric 
acid  and  the  resulting  solution  of  ferrous  and  chromic  chlorides 
is  nearly  neutralized  with  sodium  carbonate  and  an  excess  of 
barium  carbonate  added.  The  chromium  is  thus  precipitated  as 
chromic  hydroxide  together  with  a  little  ferric  hydroxide  formed 
by  atmospheric  oxidation  but  the  greater  part  of  the  iron  remains 
in  solution  as  ferrous  chloride.  The  precipitate  is  fused  with 
sodium  carbonate  and  potassium  nitrate.  In  this  way  the 
chromium  is  oxidized  to  water-soluble  alkali  chromate.  The 
aqueous  extract  is  treated  with  a  little  hydrogen  peroxide,  to 
reduce  any  permanganate  that  may  have  been  formed,  and  the 
chromium  determined  either  colorimetrically  by  comparison 
with  a  standard  sodium  chromate  solution,  or  volumetrically  by 
treating  with  an  excess  of  standard  ferrous  solution  and  deter- 
mining the  excess  by  titration  with  permanganate. 

Solutions  Required. — Hydrochloric  Acid,  approximately  6- 
normal.  (See  pp.  136,  148.) 

Sodium  Carbonate. — (See  p.  55.) 

Barium  Carbonate  Suspension. — Ten  grams  in  100  c.c.  water. 

Standard  Sodium  Chromate. — Dissolve  6.58  g.  of  sodium 
chromate,  Na2CrO4.10H2O,  in  1,000  c.c.  of  distilled  water.  One 

1  Am.  Soc.  Testing  Materials,  1916,  222,  233. 

150 


CHROMIUM  151 

cubic  centimeter  =  0.001  g.  Cr  =  0.02  per  cent  Cr  when  a  5-g. 
sample  is  used  for  analysis. 

Standard  Potassium  Permanganate. — (See  p.  158.) 

Ferrous  Sulfate. — (See  p.  158.) 

Procedure. — Dissolve  5.00  g.  of  steel  in  50  c.c.  of  the  hydro- 
chloric acid  contained  in  a  300-c.c.  Erlenmeyer  flask.  When  the 
steel  is  all  dissolved,  carefully  add  sodium  carbonate  solution 
until  nearly  all  the  free  acid  is  neutralized;  finish  the  neutral- 
ization with  barium  carbonate  suspension,  adding  about  1  g.  of 
barium  carbonate  in  excess.  Boil  the  solution  gently  for  10  or  15 
min.  with  a  small  watch-glass  on  the  flask,  to  prevent  oxidation 
of  the  iron.  Filter  rapidly  through  paper  and  wash  the  precipi- 
tate twice  with  hot  water.1  Transfer  the  filter  and  its  contents 
to  a  platinum  crucible,  burn  off  the  paper  carefully  and  fuse  the 
ash  with  a  mixture  of  5  g.  sodium  carbonate  and  0.25  g.  potassium 
nitrate.  Dissolve  the  fusion  in  water,  transfer  to  a  beaker  and 
add  2  c.c.  of  3  per  cent  hydrogen  peroxide.  Boil  a  few  minutes 
to  decompose  the  excess  of  peroxide  and  filter.  Complete  the 
determination  of  the  chromium  by  treating  the  filtrate  by  either 
of  the  following  methods. 

1.  If   the    solution    is    deep    yellow  in  color  add   10  c.c.   of 
18-normal  sulfuric  acid  (1  vol.  cone,  acid  to  1  vol.  water)  and  a 
measured  volume   of  standard  ferrous  sulfate  solution.     Cool 
thoroughly  and  titrate  with  the  standard  permanganate.     The 
number  of  cubic  centimeters  of  permanganate  used  subtracted 
from  the  volume  of  permanganate  equivalent  to  the  total  ferrous 
sulfate  used,  gives  the  volume  of  permanganate  equivalent  to 
the  chromium  in  the  sample.     One  cubic  centimeter  of  normal 
KMnO4    =    0.01733  g.  chromium.     Or,  the  chromium  value  of 
the  permanganate  may  be  obtained  by  multiplying  the  value 
of    1    c.c.    of    permanganate  in  terms   of  sodium   oxalate   by 

2Cr 

OAT    0  ^     =  0.2584. 
3Na2C204 

2.  If  the  solution  is  a  light  yellow,  cool  and  transfer  to  a  100- 
c.c.   Nessler   tube.     Then,   in   another   Nessler   tube,    dilute   a 
carefully  measured  quantity  of  standard  chromate  solution  with 
a  measured  volume  of  water  until  the  two  solutions  appear  of 

1  As  the  ferrous  iron  in  the  filtrate  oxidizes,  a  basic  ferric  salt  will  precipi- 
tate; this  precipitate  will  not  contain  any  chromium. 


152  CHEMICAL  ANALYSIS  OF  METALS 

equal  concentration  when  viewed  horizontally.  Then,  as  the 
concentration  of  the  chromium  in  one  tube  is  known,  it  is  easy  to 
compute  the  chromium  content  in  the  other  tube. 

NOTES. — In  the  titration  method  it  is  important  that  all  the 
hydrogen  peroxide  be  destroyed  by  boiling  the  alkaline  solution. 
If  left  in  the  solution  it  will  cause  the  results  to  come  out  high. 
In  alkaline  solution  the  peroxide  forms  sodium  peroxide  which 
on  boiling  decomposes  into  sodium  hydroxide  and  oxygen. 

The  above  procedure  is  recommended  by  the  American  Society 
for  Testing  Materials  for  the  analysis  of  plain  carbon  steels. 
The  method  recommended  for  the  analysis  of  alloy  steels,  which 
are  likely  to  contain  considerably  more  chromium,  is  the  same 
in  principle  except  that  a  1-g.  sample  is  used,  the  steel  is  dissolved 
in  50  c.c.  of  sulfuric  acid  (1:3),  the  barium  carbonate  is  replaced 
by  magnesium  carbonate  and  the  final  titration  is  made  with 
tenth-normal  potassium  bichromate  solution.  Several  portions 
of  magnesium  carbonate  are  added,  taking  care  that  2  or  3  g. 
of  solid  are  left  undissolved  after  the  boiling  is  completed.  When 
considerable  chromium  is  present,  it  is  well  to  titrate  directly 
with  freshly  standardized,  approximately  tenth-normal  ferrous 
sulfate  solution,  using  potassium  ferricyanide  solution  (0.1  g. 
in  50  c.c.  water,  freshly  prepared)  as  outside  indicator;  a  blue 
color  is  obtained  as  soon  as  a  slight  excess  of  ferrous  iron  is 
present.  The  use  of  hydrochloric  acid  to  dissolve  the  alloy 
steel  (a  large  excess  should  be  avoided)  and  barium  carbonate 
to  precipitate  the  chromium,  is  permissible. 

2.  DETERMINATION  OF  CHROMIUM  BY  THE  METHOD  OF  BARBA 

MODIFIED1 

Principle. — The  chromium  is  oxidized  to  chromic  acid  in  sul- 
furic acid  solution  by  means  of  potassium  permanganate,  the 
excess  of  the  latter  is  reduced  by  making  the  solution  ammoniacal 
and  boiling,  and  the  chromium  is  determined  by  the  ferrous  sul- 
fate-permanganate  method. 

Solutions  Required. — Sulfuric  Acid. — (See  p.  151.) 

Nitric  Acid.— (See  p.  92.) 

Strong  Potassium  Permanganate. — (See  p.  92.) 

Standard  Potassium  Permanganate. — (See  p.  158.) 

Ferrous  Sulfate.— (See  p.  158.) 

1  Iran  Age,  62,  153.     Am.  Soc.  Testing  Materials,  1916,  236. 


CHROMIUM  153 

Procedure. — Dissolve  1.25  g.  of  steel  in  50  c.c.  of  the  sulfuric 
acid.  If  an  insoluble  residue  remains  it  should  be  examined 
for  chromium  by  fusing  it  with  an  alkaline  flux,  as  in  the  pre- 
ceding method,  to  see  if  any  chromate  is  formed.  When  the 
steel  is  all  dissolved,  add  5  c.c.  of  the  nitric  acid  and  boil  till  the 
solution  is  clear  and"  free  from  oxides  of  nitrogen.  Dilute  with 
hot  water  to  approximately  150  c.c.,  heat,  and,  while  boiling, 
add  the  strong  permanganate  solution  until  a  permanent  brown 
precipitate  of  manganese  dioxide  is  formed.  A  large  excess  of 
permanganate  should  be  avoided,  since  the  manganese  dioxide 
is  likely  to  absorb  some  of  the  manganese.  Complete  the  analysis 
by  either  one  of  the  following  methods : 

(A)  Add  25  c.c.  of  ammonium  hydroxide  (d.  0.90)  pouring  it 
down  the  sides  of  the  beaker.     Stir  well  and  replace  the  beaker 
on  a  cooler  part  of  the  hot  plate  to  avoid  "bumping."     Stir 
occasionally  and  digest  about  15  min.,  or  until  the  permanganate 
is  all  decomposed.     Add  cautiously  20  c.c.  of  the  sulfuric  acid 
and  bring  to  a  gentle  boil.     Then  cool  the  solution  to  room 
temperature  and  transfer  to  a  250-c.c.  flask.     Make  up  to  the 
mark  and  mix  thoroughly  by  pouring  the  solution  back  and  forth 
into  a  beaker  several  times.     Filter  through  a  dry  filter  into  a 
dry  beaker,  rejecting  the  first  few  cubic  centimeters  and  use  an 
aliquot  part  of  the  filtrate,  usually  200  c.c.  (=  1  g.  of  the  steel). 

Determine  the  chromium  by  adding  ferrous  sulfate  and  titrat- 
ing the  excess  with  permanganate  (cf.  p.  158). 

(B)  Add  100  of  6-normal  hydrochloric  acid  and  boil  until  the 
solution  is  clear  and  all  the  free  chlorine  is  expelled.     Cool,  di- 
lute to  300  c.c.,  add  a  measured  quantity  of  standard  ferrous 
sulfate  solution  and  titrate  the  excess  with  permanganate. 

3.  DETERMINATION  OF  CHROMIUM  BY  THE  CHLORATE  METHOD 

Principle. — When  an  alkali  chlorate  is  added  to  a  fairly  concen- 
trated solution  of  nitric  acid,  chloric  acid  is  set  free  which  is  an 
energetic  oxidizing  agent;  manganese  is  oxidized  to  insoluble 
dioxide  and  chromic  ions  are  oxidized  to  soluble  chromic  acid:1 

3HC1O3  +  Cr+++  +  H20  -*  H2Cr04  +  3C1O2  +  3H+ 
1  If  the  concentration  of  the  nitric  acid  is  the  same  as  that  recommended 
in  the  Ford- Williams  method,  and  considerable  chromium  is  present,  the 
C1O2  is  likely  to  explode  unless  the  heating  is  done  on  a  water  bath. 


154  CHEMICAL  ANALYSIS  OF  METALS 

Solutions  Required. — Nitric  Acid. — (See  p.  57.) 

Potassium-ferricyanide  Indicator. — Dissolve  0.1  g.  of  pure  potas- 
sium ferricyanide  in  50  c.c.  of  distilled  water.  The  indicator 
solution  must  be  prepared  fresh  daily. 

Standard  Potassium  Bichromate. — Dissolve  5  g.  of  the  solid 
in  1,000  c.c.  of  distilled  water  and  standardize  against  pure  fer- 
rous ammonium  sulf ate  crystals.  Since  the  equivalent  weights 
of  ferrous  ammonium  sulfate  and  of  chromium  are  392  and  17.33, 
the  value  of  1  c.c.  of  the  solution  in  terms  of  ferrous  ammonium 
sulfate  multiplied  by  17.33/392  =  0.4421  gives  the  value  in 
terms  of  chromium. 

Standard  Potassium  Permanganate. — (See  p.  158.) 

Standard  Ferrous  Sulfate. — (See  p.  158.) 

Procedure. — Weigh  1  g.  of  steel  into  a  300-c.c.  Erlenmeyer 
flask  and  dissolve  in  30  c.c.  of  the  nitric  acid.  Evaporate 
rapidly  to  approximately  15  c.c.  and  add  50  c.c.  of  concentrated 
nitric  acid,  d.  1.42,  and  1  g.  of  sodium  chlorate  (or  potassium 
chlorate).  Evaporate,  by  boiling,  to  approximately  30  c.c.  and 
complete  the  analysis  by  either  of  the  following  procedures: 

1.  Dilute  the  solution  with  100  c.c.  of  water,  filter  off  the 
manganese  dioxide  using  an  asbestos  filter  (cf.  p.  58)  and  wash 
the  filter  with  hot  water.     Cool  the  filtrate,  dilute  with  cold 
water  to  about  600  c.c.  and  titrate  against  the  standard  ferrous 
sulfate  (the  concentration  of  which  has  been  determined  on  the 
same  day)   using  potassium  ferricyanide  as  outside  indicator. 
Or,  an  excess  of  the  ferrous  sulfate  solution  may  be  added  and 
the  excess  determined  by  titrating  back  with  standard  potassium 
bichromate  solution. 

2.  Proceed  exactly  as  in  Method  2,  Modification  B,  p.  153. 
4.  DETERMINATION  OF  CHROMIUM  BY  THE  BISMUTHATE 

METHOD 

Principle. — In  cold  solutions  containing  20  to  40  per  cent  of 
concentrated  nitric  acid,  manganese  can  be  oxidized  from  the 
bivalent  to  heptavalent  condition.  Chromium  is  oxidized  so 
slowly  under  such  conditions  that,  if  the  solution  is  promptly 
filtered,  the  manganese  may  be  titrated  by  the  ferrous  sulfate- 
permanganate  method  (cf.  p.  52).  In  hot  solutions  permanganic 
acid  in  contact  with  sodium  bismuthate  is  decomposed,  usually 


CHROMIUM  155 

forming  manganese  dioxide,  and  chromium  is  oxidized  from  the 
trivalent  to  hexavalent  condition.  In  hot  solutions,  therefore, 
chromium  can  be  determined  by  the  ferrous-sulfate-permanga- 
nate  method,  without  the  manganese  doing  any  harm.  Some 
chemists,  in  fact,  have  intentionally  added  manganese  to  the 
solution  because  manganese  dioxide  will  oxidize  chromium. 

Procedure. — Dissolve  3  g.  of  steel,  or  less  if  the  sample  contains 
more  than  1  per  cent  Cr,  in  a  250-c.c.  Erlenmeyer  flask  with  50  c.c. 
of  nitric  acid  (d.  1.13  =  25  per  cent  cone,  acid  by  vol.).  If 
there  is  any  carbonaceous  residue,  as  in  the  analysis  of  cast  irons, 
it  should  be  filtered  off  and  examined  for  chromium  by  fusion  with 
an  alkaline  oxidizing  flux  (cf.  p.  151).  If  the  metal  is  difficultly 
soluble  in  nitric  acid,  it  is  sometimes  necessary  to  add  sulfuric 
acid  to  facilitate  solution. 

When  the  sample  is  all  dissolved,  cool  the  solution  slightly 
(65  to  75°)  and  add  2  g.  of  sodium  bismuthate.  Agitate  a  few 
minutes  and  then  wash  down  the  sides  of  the  flask  with  a  little 
water.  Heat  to  boiling  and  boil  gently  until  the  permanganate 
formed  from  the  manganese  in  the  steel  is  all  decomposed  as 
shown  by  the  color;  this  usually  requires  about  15  min.  Add 
50  c.c.  of  3  per  cent  nitric  acid  (3  c.c.  HNO3,  d.  1.42 :  100  c.c. 
water)  and  filter  off  any  precipitated  manganese  dioxide  or  undis- 
solved  sodium  bismuthate  on  an  asbestos  filter.  Wash  the 
residue  three  times  with  50-c.c.  portions  of  the  dilute  nitric 
acid.  Cool  to  room  temperature  by  running  tap  water  over 
the  flask  and  dilute  with  distilled  water  to  500  c.c.  Add  a 
measured  excess  of  ferrous  sulfate  solution  and  titrate  the  excess 
with  standard  permanganate  as  described  on  p.  158. 

5.  DETERMINATION   OF   CHROMIUM  BY  THE  ETHER  METHOD 

Principle. — In  the  trivalent  condition,  chromium,  like  man- 
ganese, nickel,  cobalt  and  aluminium,  may  be  separated  from 
ferric  iron  by  shaking  the  hydrochloric  acid  solution,  of  suitable 
concentration,  with  ether.  In  the  solution  which  has  been  freed 
from  the  greater  part  of  the  iron,  the  trivalent  chromic  ions  may 
be  oxidized  to  hexavalent  chromic  acid  ions  and  the  chromium 
can  then  be  determined  either  gravimetrically  or  volumetrically. 

Necessary  Apparatus  and  Solutions. — The  necessary  apparatus 
and  solutions  including  the  Rothe  shaking  funnel,  ether-hydro- 


156  CHEMICAL  ANALYSIS  OF  METALS 

chloric  acid  solutions,  and  platinum  dish,  have  already  been 
described  under  Manganese,  p.  71. 

According  to  the  method  chosen  for  the  final  determination  of 
the  chromium,  various  other  solutions  are  necessary.  If  the 
chromium  is  to  be  determined  iodometrically,  a  standardized 
tenth-normal  solution  of  sodium  thiosulfate  is  needed;  if  it  is  to 
be  determined  by  the  permanganate  method,  standardized  solu- 
tions, of  potassium  permanganate  and  ferrous  sulfate  are  neces- 
sary. To  determine  the  chromium  gravimetrically,  the  method 
to  be  described  requires  a  solution  of  mercurous  nitrate. 

PREPARATION  AND  STANDARDIZATION  OF  TENTH-NORMAL  SODIUM 
THIOSULFATE  SOLUTION 

Dissolve  124.5  to  125  g.  of  pure  sodium  thiosulfate  crystals, 
Na2S2O3  5H2O,  in  water  that  has  been  boiled  to  expel  carbonic 
acid  and  then  cooled.  The  solution  may  be  standardized 
against  potassium  permanganate  solution  which  has  been 
titrated  against  pure  sodium  oxalate.  The  procedure  is  the  same 
as  was  described  under  Manganese,  p.  62,  for  the  standardiza- 
tion of  permanganate  against  iodine  solution.  Another  excellent 
method  of  standardizing  the  thiosulfate  solution  is  to  titrate  it 
against  pure  iodine. 

To  prepare  the  pure  iodine,  mix  5  to  6  g.  of  pure,  commercial 
iodine  crystals  with  2  g.  of  potassium  iodide,1  place  the  mixture 
in  a  dry  beaker  of  150  to  300-c.c.  capacity  and  cover  the  beaker 
with  a  300-c.c.  round-bottomed  flask,  filled  with  water  at  the  room 
temperature.  Heat  the  bottom  of  the  beaker  over  wire  gauze 
by  means  of  a  small  gas  flame.  In  a  short  time  the  greater  part 
of  the  iodine  will  have  sublimed  from  the  bottom  of  the  beaker 
and  will  have  condensed  upon  the  colder  bottom  of  the  round- 
bottomed  flask.  Scrape  the  iodine  crystals  into  a  fresh  beaker 
and  repeat  the  sublimation  without  the  use  of  potassium  iodide, 
in  order  to  get  a  perfectly  pure  product.  Break  up  the  crystals 
obtained  by  the  second  sublimation  by  pressing  them  with  a 
pestle  in  an  agate  mortar,  place  them  on  a  watch-glass  and  dry 

1  The  iodide  should  be  free  from  iodate,  as  shown  by  dissolving  a  little  of 
it  and  adding  a  little  pure  hydrochloric  acid;  no  iodine  should  be  set  free  to 
color  starch  solution. 


CHROMIUM  157 

in  a  desiccator  over  calcium  chloride  for  24  hr.;  the  top  of  the 
desiccator  should  not  be  greased.1 

Place  2  g.  of  pure  potassium  iodide  and  not  over  0.5  c.c.  of 
water  in  a  small  glass-stoppered  weighing  tube  and  weigh  care- 
fully to  0.1  mg.  Open  the  stopper  and  introduce  about  0.5  g.  of 
the  purified  and  dried  iodine,  which  dissolves  quickly  in  the  con- 
centrated potassium  iodide  solution,  insert  the  stopper  and 
weigh  again. 

Hold  the  weighing  tube  over  a  500-c.c.  Erlenmeyer  flask  con- 
taining about  1  g.  of  pure  potassium  iodide  dissolved  in  200  c.c. 
of  water.  Open  the  stopper  of  the  weighing  tube  and  at  once 
drop  the  tube  and  its  contents  into  the  dilute  potassium  iodide 
solution.  In  this  way  there  is  no  chance  of  losing  an  appreciable 
quantity  of  iodine  by  vaporization.  Titrate  the  iodine  with 
tenth-normal  sodium  thiosulfate  until  the  iodine  color  fades  to  a 
pale  yellow,  then  add  2  c.c.  of  freshly  prepared  starch  solution2 
and  continue  adding  the  sodium  thiosulfate  solution,  drop  by 
drop,  till  the  blue  color  just  disappears. 

During  the  titration,  the  following  reaction  takes  place: 

I2  +  2Na2S2O3  =  Na2S4O6  +  2NaI 

If  the  sodium  thiosulfate  solution  is  exactly  tenth-normal,  1 
liter  of  it  will  react  with  exactly  one-tenth  the  atomic  weight  of 
iodine,  or  1  c.c.  is  equivalent  to  0.01269  g.  iodine.  It  is  usually 
not  worth  while  to  make  the  solution  exactly  tenth-normal.  By 
dividing  the  weight  of  iodine  neutralized  by  1  c.c.  by  0.1269, 
the  relation  of  the  solution  to  the  normal  solution  can  be  obtained 
and  this  value  may  be  called  the  normality  of  the  solution. 
The  inconvenience  resulting  from  the  use  of  such  a  fraction  is 
very  slight. 

The  reaction  between  the  chromate  and  iodide  ions  in  acid 
solution  may  be  expressed  as  follows: 

2Cr04=  +  61-  +  16H+  =  2Cr+++  +  8H2O  +  3I2 

This  equation  shows  that  1  atom  of  chromium  is  equivalent 
to  3  atoms  of  iodine  or  1  c.c.  of  normal  sodium  thiosulfate 

1  Grease  is  likely  to  be  attacked  by  the  iodine  vapor  forming  hydriodic 
acid  which  may  contaminate  the  iodine  crystals. 

2  The  starch  solution  is  prepared  by  dissolving  0.5  g.  of  soluble  starch 
in  25  c.c.  of  hot  water.     It  is  ready  for  use  as  soon  as  it  cools. 


158  CHEMICAL  ANALYSIS  OF  METALS 

solution  is  equivalent  to  0.01733  g.  of  Cr.  By  multiplying  this 
last  value  by  the  value  expressing  the  relation  of  the  sodium 
thiosulfate  solution  to  the  normal  solution,  i.e.,  its  normality,  the 
value  of  1  c.c.  of  the  thiosulfate  solution  in  terms  of  chromium 
is  obtained. 

Preparation  and  Standardization  of  Permanganate  and  Ferrous 
Sulfate  Solutions. — A  suitable  solution  of  permanganate  may  be 
prepared  by  dissolving  about  16  g.  of  potassium  permanganate 
in  5  liters  of  water.  The  preparation  and  standardization  of 
such  a  solution  was  discussed  under  Manganese,  p.  61. 

To  prepare  a  ferrous  sulfate  solution  of  corresponding  concen- 
tration, dissolve  60  g.  of  pure  ferrous  sulfate  crystals,  FeSO4  TEUO 
in  water,  add  100  c.c.  of  concentrated  sulfuric  acid,  and  dilute  to 
2  liters. 

The  ferrous  sulfate  solution  is  not  very  stable  but  gradually 
weakens  owing  to  the  slow  oxidation  of  the  ferrous  ions.  For 
this  reason,  its  strength  compared  with  that  of  the  permanga- 
nate must  be  determined  on  the  same  day  that  the  analysis  for 
chromium  is  made.  Measure  out  a  portion  of  the  solution  by 
means  of  a  pipette,  dilute  to  100  c.c.  and  titrate  with  perman- 
ganate. Use  the  same  quantity  of  ferrous  sulfate  as  in  the 
analysis  for  chromium.  The  quantity  chosen  must  be  sufficient 
to  react  with  all  the  chromium  present  so  that  an  excess  remains 
to  be  titrated  with  permanganate.  Then,  by  subtracting  the 
volume  of  permanganate  used  in  titrating  the  excess  of  ferrous 
sulfate  in  an  analysis,  from  the  volume  of  permanganate  which 
has  been  found  to  be  required  for  all  of  the  ferrous  sulfate  used, 
the  difference  gives  the  volume  of  permanganate  which  is 
equivalent  to  the  chromium  in  the  sample. 

The  reaction  between  the  chromate  and  ferrous  ions  may  be 
expressed  as  follows: 

CrO4—  +  3Fe++  +  8H+  =  Cr+++  +  3Fe+++  +  4H2O 
The  reaction  between  ferrous  and  permanganate  ions  is: 
MnO4-  +  5Fe++  +  8H+  =  Mn++  +  5Fe+++  +  4H2O 

Since  the  change  in  valence  of  the  chromium  is  three,  it  is  clear 

that  1   c.c.  of  normal  permanganate  is  equivalent  to  Q  nnn   = 

o,UUU 

0.01733  g.  Cr,  as  in  the  titration  with  sodium  thiosulfate. 


CHROMIUM  159 

In  the  standardization  of  the  permanganate  against  sodium 
oxalate  the  reaction  is 

5C2O4—  +  2MnO4-  +  16H+  =  10CO2  +  2Mn++  +  8H2O 

If  n  c.c.  of  permanganate  are  used  in  titrating  p.  g.  of  sodium 
oxalate  then   the   normality  of  the   permanganate  solution  is 

P___  P 

Na2C2O4      0.067n 


and  the  value  of  1  c.c.  permanganate  in  terms  of  chromium  is 

0.01733  X  p     P09,o7o.  Pr 
"aOGT^r  =  ^2587  g.Cr 

Mercurous  Nitrate  Solution. — Pulverize  100  g.  of  pure  mer- 
curous  nitrate  and  shake  it  with  water  in  a  glass-stoppered  liter 
bottle. 

To  prevent  oxidation,  add  a  little  pure  mercury.  The  mer- 
curous  nitrate  is  hydrolyzed  to  some  extent  so  that  the  solu- 
tion always  contains  free  acid  and  some  basic  mercurous  nitrate 
remains  at  the  bottom  of  the  bottle. 

Procedure. — Of  pig  iron  and  steel  with  low  chromium  con- 
tent take  10  to  15  g.,  of  richer  materials  4  to  5  g.  Dissolve  the 
sample  in  a  porcelain  dish  with  dilute  nitric  acid1  (d.  1.2), 
evaporate  to  dryness,  destroy  the  nitrates,  take  up  with  hydro- 
chloric  acid  and  remove  the  silica  as  in  Method  3,  p.  121. 2 

The  silica  frequently  holds  back  a  little  chromium.  After 
volatilizing  the  silica  with  sulfuric  and  hydrofluoric  acids,  there- 
fore, test  for  chromium.  Mix  it  in  the  platinum  crucible  with 
a  little  magnesia-sodium-carbonate  mixture  (cf.  p.  125)  and  heat 
strongly  for  ^  nr-  Extract  the  product  obtained  with  hot  water 
to  dissolve  the  sodium  chromate.  Filter  off  the  residue  and  acidify 
the  nitrate  with  hydrochloric  acid.  Add  about  0 . 25  g.  of  potas- 
sium iodide  and  titrate  any  liberated  iodine  with  the  tenth- 
normal  sodium  thiosulfate  solution.  Instead  of  titrating  the 

1  Some  samples  of  materials  rich  in  chromium  do  not  dissolve  readily  in 
nitric  acid;  in  such  cases  concentrated  hydrochloric  acid,  without  the  use  of 
an  oxidizing  agent,  may  be  used.     If  this  dissolves  the  sample,  evaporate 
to  dryness,  remove  the  silica  by  Method  1,  p.  115,  oxidize  the  iron  with 
nitric  acid  and  prepare  for  the  ether  separation  in  the  usual  way. 

2  To  hasten  the  process,  the  procedure  described  on  p.  88,  may  be  used. 


160  CHEMICAL  ANALYSIS  OF  METALS 

sodium  chromate,  it  can  be  treated  as  described  on  p.  162  and 
the  chromium  weighed  as  oxide. 

Evaporate  the  nitrate  from  the  silica,  and  shake  with  ether 
as  described  on  p.  73. 

Precipitate  the  copper  as  sulfide  from  the  hydrochloric  acid 
solution  and  in  the  nitrate  carry  out  the  treatment  with  caustic 
soda  and  sodium  peroxide  as  described  on  p.  76. 

Treat  the  fusion  in  the  platinum  dish  with  water;  all  the  chro- 
mium goes  into  solution  as  sodium  chromate  and  part  of  the 
manganese  dissolves  as  sodium  manganate,  imparting  a  green 
color  to  the  solution.  In  case  the  excess  of  sodium  peroxide  used 
is  insufficient  to  convert  the  manganese  to  manganese  dioxide  on 
boiling  the  solution,1  add  one  or  two  knife-bladefuls  more  of  this 
reagent,  stir  well  and  cover  with  a  watch-glass. 

Transfer  the  solution  to  a  300-c.c.  beaker,  dilute  with  water  to 
about  200  c.c.,  and  allow  the  precipitate  to  settle  while  heating 
on  the  water  bath.  Cool,  filter  the  clear  solution,  which  is 
colored  more  or  less  yellow  according  to  the  quantity  of  chromium 
present,  and  wash  the  precipitate,  which  contains  all  the  man- 
ganese, nickel,  cobalt  and  residual  iron,  with  hot  water  until 
the  washings  are  no  longer  alkaline  to  litmus.  The  precipitate 
may  be  used  for  the  determination  of  manganese,  nickel  and 
cobalt.  The  aqueous  solution  may  contain  besides  sodium 
chromate,  some  sodium  phosphate  and  sodium  vanadate  accord- 
ing to  the  extent  that  these  elements  are  present  in  the  original 
material.  If  vanadate  is  present  it  interferes  somewhat  with  the 
iodometric  determination  of  the  chromium,  as  it  is  reduced  slowly 
by  means  of  hydriodic  acid.  It  is  hard  to  get  a  good  end-point 
with  sodium  thiosulfate  and  the  results  for  chromium  are  too 
high. 

It  is  also  claimed  that  vanadic  acid  influences  the  volumetric 
estimation  of  the  chromium  when  ferrous  sulfate  and  potassium 
permanganate  are  used  in  the  titration,  though  Campagne  has 
shown  that  good  results  can  be  obtained  in  the  presence  of 
vanadium. 

It  is  safer  to  remove  the  vanadium  before  attempting  to  titrate 
the  chromium. 

By   treating   the   aqueous   solution   with   mercurous   nitrate 

1  In  such  cases  purple  permanganate  i°ns  are  usually  present. 


CHROMIUM  161 

solution,  mercurous  chromate,  phosphate  and  vanadate  are 
precipitated. 

To  recover  the  chromium  in  it,  this  precipitate  must  be  fil- 
tered off,  the  filter  and  precipitate  ignited,  the  mercury  volatil- 
ized and  the  residue  subjected  to  a  suitable  fusion  process 
(c/.  pp.  76,  163,  165). 

If  the  chromate  solution  shows  only  a  slight  pale  yellow  color, 
the  whole  of  it  may  be  taken  for  the  chromium  titration.  If 
much  chromium  is  present,  as  shown  by  a  deep  yellow  color, 
transfer  the  solution  to  a  500-c.c.  calibrated  flask  and  take  an 
aliquot  part,  e.g.,  50  c.c.  for  the  titration. 

It  is  not  advisable  to  attempt  to  titrate  more  than  0.1  g.  of 
chromium  or  the  solutions,  toward  the  end  of  the  titration,  will 
become  so  green  with  chromic  ions  that  it  is  difficult  to  detect 
the  correct  end-point.  This  is  true  whether  the  determination 
is  carried  out  by  the  iodometric  method  or  by  means  of  ferrous 
sulfate  and  permanganate.  When  strongly  colored,  it  is  neces- 
sary to  dilute  largely  before  titrating. 

(a)  Iodometric  Determination  of  Chromium. — Before  acidifying 
the  alkaline  chromate  solution,  it  is  necessary  to  decompose  the 
excess  sodium  peroxide  by  boiling.  If  any  of  it  is  left  undecom- 
posed,  hydrogen  peroxide  is  formed  on  making  the  solution  acid. 
This  may  unite  with  the  chromic  acid  to  form  blue  perchromic 
acid  which  is  not  very  stable  and  decomposes  readily  into  chromic 
salt.  Some  of  the  chromium,  therefore,  is  likely  to  miss  the 
titration  if  any  hydrogen  peroxide  is  formed.  After  decomposing 
all  the  excess  of  sodium  peroxide,  transfer  the  solution  to  a  600- 
c.c.  Erlenmeyer  flask,  acidify  the  cold  solution  with  hydrochloric 
acid,  and  add  1  g.  of  pure  potassium  iodide,  which  must  be 
free  from  iodate.1  Dilute  to  about  200  to  300  c.c.  and  titrate 
with  thiosulfate  solution  until  the  iodine  color  fades  to  a  pale 
yellow,  then  add  2  c.c.  of  starch  solution  and  titrate  till  the  blue 
color  just  disappears. 

Computation. — If  in  the  analysis  of  s  g.  of  material,  n  c.c.  of 
/-normal  thiosulfate  solution  were  used,  including  that  required  for 
titrating  the  chromium  found  in  the  residue  from  the  silica,  then 


per  cent  Cr  =  1.733  /- 


1  c/.  pp.  63,  156. 
11 


162  CHEMICAL  ANALYSIS  OF  METALS 

The  value  /,  as  described  on  p.  55,  is  obtained  by  dividing  the 
value  of  1  c.c.  of  the  sodium  thiosulfate  solution  in  terms  of  the 
substance  against  which  it  is  standardized  by  the  value  of  1  c.c. 
of  a  normal  solution  of  sodium  thiosulfate  in  terms  of  the  same 
substance. 

(/3)  Titration  with  Ferrous  Sulfate  and  Permanganate. — To 
the  chromate  solution  freed  from  excess  of  sodium  peroxide,  as  in 
Method  a,  add  dilute  sulfuric  acid  (1:10)  in  moderate  excess  and 
dilute  the  solution  to  about  300  c.c.  Add,  by  means  of  a  pipette, 
25  or  50  c.c.  of  ferrous  sulfate  solution.  Enough  ferrous  sulfate 
must  be  used  to  reduce  all  of  the  yellow  chromate  ion  to  green 
chromic  ion.  If  more  than  50  c.c.  are  required  to  accomplish 
this  reduction,  it  is  advisable  to  work  with  a  smaller  sample, 
obtained  by  taking  an  aliquot  part  of  the  solution  as  already 
described. 

Then,  without  allowing  the  solution  to  stand  very  long,  titrate 
slowly  with  permanganate.  Titrate  a  fresh  portion  of  the  ferrous 
sulfate  solution  alone  against  the  permanganate,  using  the  same 
pipette  that  was  used  in  the  analysis. 

Computation. — If  a  c.c.  of  /-normal  permanganate  were  used 
in  titrating  a  pipetteful  of  ferrous  sulfate  and  b  c.c.  of  perman- 
ganate were  used  in  the  analysis  of  s  g.  of  material,  then 

1.733/(a  -b) 
per  cent  Cr  =  - 

s 

or,  if  T  represents  the  value  of  1  c.c.  permanganate  in  terms  of 
chromium  (pp.  158,  159). 

n         100  T  (a  -  b) 
per  cent   Cr  =  - 

(7)  Precipitation  with  Mercurous  Nitrate  Solution. — For  the 
chromium  determination  use  all  or  a  part  of  the  nitrate  from  the 
fusion  with  sodium  peroxide  (p.  160)  according  to  the  amount 
of  chromium  present. 

Transfer  the  solution  to  a  300  to  400-c.c.  beaker  and  cautiously 
neutralize  it  with  dilute  nitric  acid.  Stop  adding  the  acid  as  soon 
as  a  piece  of  litmus  paper  in  the  solution  assumes  a  wine-red  color. 
Then  add  mercurous  nitrate  solution,  cover  the  beaker  with  a 
watch-glass  and  boil  the  solution  a  short  time.  Allow  the 
precipitate,  which  is  gray  or  grayish  green  when  thrown  down 


CHROMIUM  163 

from  faintly  alkaline  solutions,  and  red  (or  yellow)  when  thrown 
down  from  faintly  acid  solutions,  to  settle  to  the  bottom  of  the 
beaker  and  test  with  more  mercurous  nitrate  solution  to  see  if 
the  precipitation  is  complete. 

The  mercurous  nitrate  solution  is  always  slightly  acid  as  a 
result  of  the  hydrolysis,  so  that,  when  much  of  the  reagent  is 
added,  the  solution  may  become  so  acid  that  the  precipitation 
of  the  chromic  acid  is  incomplete.  In  such  cases  a  few  drops 
of  ammonia  may  be  added  and  the  solution  again  heated.  This 
must  be  done  with  caution,  for  an  excess  of  ammonia  will  cause 
the  formation  of  soluble  ammonium  chromate  and  the  precipi- 
tation of  the  chromic  acid  will  be  incomplete.  After  the  pre- 
cipitate has  settled,  test  again  with  a  little  more  mercurous 
nitrate  solution.  Filter  off  the  precipitate  through  an  ashless 
filter  paper  and  wash  it  first  with  pure  water  and  finally  with 
very  dilute  mercurous  nitrate  solution  (25  c.c.  of  the  reagent 
diluted  to  500  c.c.).  If  it  is  intended  to  purify  the  precipitate,  it 
is  not  necessary  to  wash  it  entirely  free  from  alkali  salts. 

Ignite  the  filter  together  with  the  precipitate  in  an  open  plati- 
num crucible  under  a  good  hood  (on  account  of  the  poisonous 
vapors)  and  finally  heat  strongly.  Sometimes  the  ignited 
chromic  oxide,  Cr2O3,  which  is  formed  by  the  ignition  of  the 
mercurous  chromate,  is  pure  enough  to  weigh.  This  is  seldom 
the  case  in  the  analysis  of  steel.  Of  the  elements  likely  to  be 
present  in  steel,  mercurous  nitrate  solution  will  precipitate  the 
phosphorus  as  phosphate,  the  vanadium  as  vanadate,  the 
tungsten  as  tungstate,  and  the  molybdenum  as  molybdate.  Of 
these  elements,  phosphorus  and  vanadium  are  the  only  ones  that 
need  be  considered.  The  tungstic  acid  will  be  precipitated 
practically  completely  with  the  silica  and  will  be  left  as  a  yellow 
residue  after  the  volatilization  of  the  silicon  as  fluoride.  Molyb- 
denum follows  the  iron  in  the  ether  separation  so  that  very  little 
of  it  can  be  present  at  this  stage  in  the  analysis.  The  method 
of  purifying  the  precipitate,  however,  would  serve  equally  well 
for  separating  chromium  from  phosphorus,  vanadium,  tungsten 
and  molybdenum. 

Purification  of  the  Impure  Chromic  Oxide. — The  purification 
process  to  be  described  depends  upon  the  fact  that  it  is  possible 
by  means  of  an  alkaline  reducing  fusion  to  keep  the  chromium 


164  CHEMICAL  ANALYSIS  OF  METALS 

as  insoluble  chromic  oxide  while  converting  the  impurities  into 
soluble  alkali  salts.  A  suitable  flux  is  prepared  by  mixing  4 
parts  of  pure  double  carbonate  of  sodium  and  potassium  with  1 
part  of  pure  potassium  acid  tartrate.  Instead  of  the  double  car- 
bonate, sodium  carbonate  may  be  used.  (Another  suitable  flux 
may  be  prepared  with  sodium  carbonate  and  sodium  acetate.) 

Commercial  potassium  acid  tartrate  (cream  of  tartar)  is  likely 
to  contain  a  little  calcium  sulfate.  In  case  pure  potassium  acid 
tartrate  is  not  at  hand,  it  may  be  prepared  by  adding  a  filtered 
solution  of  150  g.  of  tartaric  acid  to  an  aqueous  solution  of 
56  g.  of  pure  caustic  potash.  Cool  the  solution,  filter  off  the 
crystals  with  the  aid  of  suction,  and  dry  them  at  105°  in  the  hot 
closet 

Mix  the  impure  chromic  oxide  in  the  platinum  crucible  with 
8  to  10  times  as  much  of  the  carbonate-tart  rate  mixture  and 
heat  with  a  moderate  flame.  The  potassium  acid  tartrate  soon 
begins  to  decompose.  Raise  the  cover  of  the  crucible  and  watch 
the  carbonization  and  fusing  together  of  the  contents.  The 
carbon  that  is  deposited  from  the  tartrate  gradually  oxidizes  to 
carbonic  oxide  gas  in  the  fusion  mixture.  As  soon  as  nearly  all 
of  the  free  carbon  is  gone,  stop  fusing. 

Special  attention  must  be  paid  to  the  proper  timing  of  the 
fusion.  If  it  is  continued  too  long,  some  of  the  chromic  oxide 
will  be  oxidized  to  chromate,  imparting  a  yellow  color  to  the 
fusion.  If  the  fusion  is  not  continued  long  enough,  some  of  the 
impurities  may  not  be  converted  to  soluble  alkali  salts. 

If  considerable  chromic  oxide  is  to  be  purified,  it  is  rather 
better  to  fuse  it  first  with  pure  sodium  carbonate  and  then  reduce 
the  chromate  by  the  addition  of  potassium  acid  tartrate  finishing 
the  treatment  as  described. 

After  cooling,  place  the  crucible  in  a  small  beaker  and  warm 
the  melt  with  a  little  water.  When  all  of  the  alkali  salts  have 
dissolved,  remove  the  crucible,  washing  it  well  with  hot  water, 
and  filter  the  solution  through  an  ashless  filter.  Chromic  oxide, 
mixed  with  some  charcoal,  remains  behind  upon  the  filter.  Wash 
the  filter  and  precipitate  thoroughly  with  hot  water  and  finally 
with  a  few  drops  of  very  dilute  nitric  acid,  to  make  sure  that 
all  the  alkali  salts  are  dissolved.  Ignite  the  precipitate  in  a 
platinum  crucible  and  weigh  the  green  chromic  oxide,  Cr2O3. 


CHROMIUM  165 

If  desired,  the  purity  of  the  chromic  oxide  may  be  verified  by 
fusing  it  with  magnesia-sodium-carbonate  mixture  (p.  125) 
dissolving  the  sodium  chromate  in  water  and  titrating  the 
chromate  in  acid  solution  by  either  Method  a  or  Method  /3. 

The  filtrate  from  the  fusion  for  the  purification  of  the  chromic 
oxide  may  be  used  for  the  determination  of  phosphorus  or  of 
vanadium. 

Computation. — If  p  g.  of  chromic  oxide  were  obtained  in  the 
analysis  of  a  sample  weighing  s  g.  then 

2  Cr  X  p  X  100      68.42p 
per  cent  Cr  =  — ^    ~    _.       -  =  — 

Cr2O3  X  s  s 

The  chromium  carried  down  by  the  silica  must  also  be  taken  into 
consideration  (p.  159). 

6.  DETERMINATION  OF  CHROMIUM  BY  FUSION  OF  THE  OXIDES 
WITH  SODIUM  PEROXIDE 

Principle. — The  sample  is  converted  into  oxide  and  the  chromic 
oxide  is  converted  to  chromate  by  fusing  with  sodium  peroxide 
in  a  nickel  or  iron  crucible.  The  method  is  suitable  for  chrome- 
steel,  chrome-nickel  steel,  chrome-tungsten  steel  and  chrome- 
vanadium  steel;  steels  with  low-chromium  content  are  analyzed 
preferably  by  one  of  the  methods  already  described,  using  a 
larger  sample. 

Procedure. — Treat  2  g.  of  the  metal  in  a  small  porcelain 
evaporating  dish  with  6-normal  nitric  acid  (d.  1.2)  evaporate 
the  solution  to  dryness,  and  heat  the  residue  until  the  nitrates 
are  decomposed,  keeping  the  dish  covered  with  a  watch-glass  to 
prevent  loss  by  spattering.  During  the  heating,  the  oxides 
are  dislodged,  for  the  most  part,  from  the  sides  of  the  dish. 
Transfer  the  loose  particles  to  an  agate  mortar,  mix  them  with 
sodium  peroxide  (about  16  g.  is  used  in  an  analysis)  and  transfer 
the  mixture  to  a  well-scoured  nickel  or  iron  crucible.1  Carefully 
scrape  off  with  a  spatula  as  much  as  possible  of  the  oxide  from 
the  porcelain  dish,  mix  it  with  sodium  peroxide  and  add  the  mix- 
ture to  the  crucible.  Next  place  a  little  sodium  peroxide  in  the 

1  A  new  iron  crucible  is  usually  covered  with  some  sort  of  varnish.  To 
remove  it,  heat  the  crucible  to  redness  over  a  Meker  burner  or  a  blast  lamp 
and  plunge  the  red  hot  crucible  into  water. 


166  CHEMICAL  ANALYSIS  OF  METALS 

dish,  rub  the  dish  with  it  and  transfer  to  the  crucible.  Finally 
add  a  little  caustic  soda  solution  to  the  dish,  heat  it  nearly  to 
boiling  and  rinse  the  solution  into  a  beaker,  setting  it  aside  for 
the  time  being. 

Cover  the  crucible  and  heat  it  with  a  small  flame  until  the  mass 
melts,  then  raise  the  temperature  and  heat  to  dull  redness  for 
about  15  min.  Allow  the  crucible  to  cool,  place  it  in  a  beaker, 
add  hot  water,  and  cover  the  beaker  with  a  watch-glass.  The 
mass  dissolves  quickly  with  decomposition  of  most  of  the  excess 
of  peroxide.  Add  the  reserved  alkali  solution  with  which  the 
evaporating  dish  was  washed,  remove  the  crucible,  washing  it 
thoroughly,  and  allow  the  beaker  and  its  contents  to  stand  an 
hour  or  two  on  the  steam  bath.  If  the  solution  should  not  be 
yellow  but  green  in  color,  owing  to  the  presence  of  manganate, 
add  a  little  sodium  peroxide  and  stir;  this  serves  to  reduce  the 
manganate  to  manganese  dioxide.  Dilute  the  solution  to  200 
c.c.,  allow  it  to  cool  and,  when  well  settled,  decant  the  super- 
natant liquid  through  a  filter,  without  disturbing  the  residue. 
Cover  the  residue  with  hot  water  and  allow  it  to  settle  again. 
Then  filter  as  before,  catching  the  filtrate  in  a  fresh  beaker  so 
that  if  any  of  it  runs  through  turbid  it  will  not  be  necessary  to 
refilter  the  entire  filtrate.  Transfer  the  residue  to  the  filter  and 
wash  it  with  hot  water  until  the  washings  are  neutral  to  red 
litmus  paper. 

A  little  chromium  is  likely  to  remain  with  the  iron  in  an  insolu- 
ble condition  such  that  it  is  impossible  to  remove  it  by  washing. 
To  recover  this  chromium,  ignite  the  precipitate  and  filter  and 
repeat  the  fusion  with  sodium  peroxide  in  exactly  the  same  man- 
ner as  before,  finally  combining  the  aqueous  extract  of  the  fusion 
with  that  first  obtained. 

Boil  the  solution  until  all  the  excess  of  sodium  peroxide  is 
destroyed,  cool  to  room  temperature  and  dilute  up  to  the  mark 
in  a  500  c.c.  calibrated  flask.  Use  an  aliquot  part,  usually  one- 
fifth,  for  the  determination  of  the  chromium  according  to  p.  161. 

If  preferred,  the  aqueous,  alkaline  solution  of  sodium  chromate 
may  be  used  for  the  gravimetric  determination  of  chromium 
according  to  p.  162.  In  that  case,  treat  the  impure  chromic 
oxide  with  sulfuric  and  hydrofluoric  acids  and  heat  to  expel  any 
silica,  before  fusing  it  with  the  alkaline  reducing  flux. 


CHROMIUM  167 

7.  DETERMINATION  OF  CHROMIUM  IN  MATERIALS  INSOLUBLE 

IN  ACID 

The  method  is  applicable  to  the  analysis  of  ferro-chrome, 
chrome-tungsten  steel,  etc. 

Procedure. — Intimately  mix  from  0.5  to  2  g.  of  the  pulverized 
sample  with  10  times  as  much  of  the  Rothe  fusion  mixture 
(p.  125),  transfer  the  mixture  to  a  platinum  crucible,  and  heat 
^2  hr.  over  a  Tirrill  burner  and  the  same  length  of  time  over  a 
large  Meker  burner,  or  over  a  blast  lamp.  Transfer  as  much  as 
possible  of  the  ignited  product  to  an  agate  mortar,  moisten  it 
with  a  little  water  and  crush  it  carefully  to  a  paste.  Rinse  the 
paste  into  a  beaker  and  heat  on  the  steam  bath  to  extract  the 
soluble  chromate.  Allow  the  residue  to  settle,  decant  the 
solution  through  a  filter,  and  wash  the  residue  by  decantation  and 
then  thoroughly  on  the  filter,  with  hot  water.  Ignite  the  filter 
and  residue  in  the  platinum  crucible  and  fuse  it  with  about  four 
times  as  much  sodium  carbonate  as  the  original  sample  weighed. 
After  cooling  the  crucible,  extract  the  soluble  sodium  salts  and 
repeat  the  fusion  with  sodium  carbonate  in  order  to  remove  the 
last  traces  of  chromium.  If  the  material  was  sufficiently  fine, 
the  quantity  of  chromium  left  in  the  residue  after  the  third  fusion 
is  perfectly  negligible. 

The  residue  may  be  used  for  the  determination  of  iron,  man- 
ganese, or  nickel. 

Combine  all  the  aqueous  extracts  and  dilute  to  500  or  1,000 
c.c.  in  a  calibrated  flask.  Take  an  aliquot  part  for  the  chro- 
mium determination,  according  to  p.  161,  bearing  in  mind  that  the 
solution  may  contain  vanadate  or  tungstate  of  sodium. 

Test  Analysis. — (1)  Separation  of  Chromium  and  Iron  by  the 
Ether  Method. — Ten  cubic  centimeters  of  a  solution  of  chromic 
chloride  was  analyzed  by  the  permanganate  process  and  found 
equivalent  to  53.5  c.c.  of  permanganate  (=  0.1083  g.  Cr). 

In  duplicate  experiments,  10  c.c.  of  the  chromic  chloride  solu- 
tion were  mixed  with  50  c.c.  of  pure  ferric  chloride  solution  ( =  4.4 
g.  Fe) ,  the  iron  removed  by  the  ether  method  and  the  chromium 
determined  by  Method  5/3,  p.  162.  In  one  experiment  53.5  c.c. 
of  permanganate  were  used  and  in  the  other  53.3  corresponding 
to  0.1083  and  0.1079  g.  Cr;  this  shows  that  the  separation  is 
accurate  within  the  usual  limits  of  error. 


168  CHEMICAL  ANALYSIS  OF  METALS 

Two  experiments  were  carried  out  with  respectively  5  and  10 
c.c.  of  another  chromic  chloride  solution  (=  0.0031  and  0.0062  g. 
Cr)  in  the  presence  of  ferric  chloride  solution  corresponding  to 
3.2  g.  Fe.  In  this  case  the  analysis  was  finished  by  titration  with 
sodium  thiosulfate  solution  and  the  values  agreed  perfectly  to 
the  two  significant  figures  given  above,  showing  that  with  low 
chromium  the  process  gives  results  agreeing  within  0.0001  g.  of 
chromium. 

2.  Analysis  of  Various  Chrome  Steels. — A  sample  of  chrome 
steel  weighing  6.000  g.  was  analyzed  by  Method  5  and  one-fifth 
of  the  solution  was  taken  for  the  final  determination.     Volu- 
metrically,  by  the  permanganate  method,  the  value  4.07  per  cent 
Cr  was  obtained  which  agreed  well  with  4.05  per  cent  Cr,  the 
value  obtained  gravimetrically. 

A  sample  of  nickel-chrome  steel,  weighing  6  g.,  was  analyzed  by 
the  sodium  thiosulfate  method,  using  two-fifths  of  the  original 
solution,  and  the  value  0.22  per  cent  Cr  was  obtained.  Another 
test  was  carried  out  with  a  6-g.  portion  of  the  steel  and  using  the 
entire  solution  for  the  final  titration.  In  this  case  the  value 
0.23  per  cent  Cr  was  obtained. 

A  sample  of  chrome-tungsten  steel  with  6  per  cent  tungsten, 
analyzed  by  Method  5/3,  gave  5.82  per  cent  Cr  and  by  Method 
5a,  5.84  per  cent  Cr.  In  this  case  0.04  per  cent  Cr  was  recov- 
ered from  the  silica. 

A  sample  of  chrome-tungsten  steel  with  4  per  cent  W,  analyzed 
by  Method  5)3,  showed  10.22  per  cent  Cr  and  by  Method  5a,  10.36 
per  cent  Cr.  In  this  case  the  chromium  from  the  silica  in 
Method  5/2  in  one  case  amounted  to  1.06  per  cent. 

A  sample  of  ferro-chrome  was  analyzed  by  Method  7.  One 
gram  of  the  substance  was  weighed  out  and  one-tenth  of  the 
solution  taken  for  the  final  titration  with  sodium  thiosulfate.  In 
duplicate  determinations  the  values  60.8  and  60.7  per  cent  Cr 
were  obtained. 

3.  Purification  of  Chromic  Oxide  Precipitates. — Ten  cubic  cen- 
timeters of  tungstate  solution  (0.2724  g.  W03)  were  mixed  with 
10  c.c.  of  chromate  solution  (0.0250  g.  Cr2O3)  and  the  solution 
precipitated  with  mercurous  nitrate.     After  purification  with 
the  potassium  acid  tartrate  mixture,  the  Cr203  obtained  weighed 
0.0252  g. 


CHROMIUM  169 

A  similar  experiment  with  vanadate  solution  (0.153  g.  V203) 
and  chromate  solution  (0.0500  g.  Cr203)  gave  0.0505  g.  of  purified 
Cr203. 

Accuracy  of  the  Results  and  Permissible  Variations. — With 
chromium  content  of  less  than  0.5  per  cent  duplicate  determina- 
tions should  agree  within  0.005  per  cent  and  with  10  per  cent 
Cr,  or  more,  the  values  should  agree  within  0.1  per  cent.  The 
values  should  also  closely  approximate  the  truth. 


CHAPTER  IX 
IRON 

In  the  analysis  of  a  sample  of  ordinary  steel  the  percentage  of 
iron  is  usually  determined  most  accurately  by  deducting  the  per- 
centages of  other  constituents  from  100.  In  the  analysis  of 
special  steels  and  ferro  alloys,  however,  it  is  often  important  to 
have  an  accurate  and  rapid  method  for  determining  the  iron 
directly.  A  great  many  methods  are  known  for  the  accurate 
determination  of  iron  but  unfortunately  nearly  all  of  them  are 
influenced  by  some  of  the  other  elements  which  are  found  in 
steel  alloys.  For  this  reason  it  is  hard  to  give  general  directions 
which  will  be  applicable  in  all  cases  and  sometimes  the  errors 
involved  in  separating  iron  from  a  number  of  possible  interfering 
elements  are  such  as  to  influence  seriously  the  final  determination. 

Thus  the  small  amount  of  carbon  present  in  the  iron  wire  that 
is  so  frequently  used  for  standardization  may  influence  the  volu- 
metric determination  to  the  extent  of  several  tenths  of  1  per  cent, 
unless  special  precautions  are  taken,  such  as  gently  boiling  the 
solution  or  oxidizing  with  strong  permanganate  before  attempting 
to  reduce  the  solution  previous  to  the  titration  with  permanga- 
nate. Similarly,  the  errors  in  the  gravimetric  determination  of 
iron  are  often  considerable.  Thus  vanadium,  titanium,  alumin- 
ium and  molybdenum  may  be  precipitated  with  ferric  oxide  and 
the  ammonia  used  may  contain  dissolved  silica  which  will  be 
precipitated  when  poured  into  the  acid  solution  and  thus  con- 
taminate the  ferric  hydroxide  precipitate.  Moreover,  there  is 
difficulty  in  igniting  the  ferric  oxide;  if  it  is  heated  too  hot,  espe- 
cially when  all  the  carbon  is  not  consumed,  some  magnetic  oxide 
is  formed,  and  if  the  precipitate  is  not  washed  free  from  chloride 
some  ferric  chloride  may  be  volatilized. 

1.  DETERMINATION  OF  IRON  IN  MATERIALS  SOLUBLE  IN  ACID 
(A)  MOHR'S  IODOMETRIC  METHOD 

The  method   depends   upon   the  reduction  of  the  iron  with 

170 


IRON  171 

potassium  iodide   in   slightly   acid  solution   and    the   titration 
of  the  liberated  iodine  with  sodium  thio-sulfate. 
2Fe  ~ 


The  determination  of  the  iron  can  usually  be  combined  with 
the  determination  of  some  other  constituent.  Thus  the  ether 
solution  obtained  in  the  determination  of  manganese,  chromium, 
nickel  and  cobalt,  aluminium,  titanium,  vanadium,  etc.,  may  be 
used  for  the  iron  determination.  If  an  ethereal  solution  of  ferric 
chloride  is  exposed  to  the  light,  particularly  direct  sunlight,  for 
any  length  of  time,  some  of  the  ferric  chloride  becomes  reduced  to 
ferrous  chloride.  In  such  cases  the  solution  should  be  oxidized 
and  the  excess  of  oxidizing  agent  removed  before  attempting  to 
determine  the  iron  by  the  iodometric  process. 

Shake  the  ethereal  solution  in  the  Rothe  shaking  funnel  with 
several  portions  of  water,  transferring  the  washings  to  a  tall 
beaker,  then  wash  a  few  times  with  dilute  hydrochloric  acid,  until 
finally  the  addition  of  a  fresh  portion  of  hydrochloric  acid  shows 
no  further  yellow  color  of  dissolved  ferric  chloride  and  the  upper 
ether  layer  is  perfectly  colorless.  Evaporate  off  the  dissolved 
ether  by  heating  on  the  water  bath  and  concentrate  to  a  small 
volume. 

Dilute  the  solution  to  500  c.c.  in  a  calibrated  flask,  mix  thor- 
oughly, and  take  an  aliquot  portion  corresponding  to  about  0.25 
g.  of  iron. 

Pour  the  slightly  acid  solution  into  a  300-c.c.  Erlenmeyer  flask, 
add  3  g.  of  pure  potassium  iodide,  free  from  iodate,  and  titrate 
the  liberated  iodine  with  tenth-normal  thiosulfate  solution.  Add 
the  thiosulfate  slowly  from  the  burette  until  only  a  slight  color 
remains  in  the  iron  solution,  then  add  2  c.c.  of  starch  solution 
(cf.  p.  63)  and  titrate  until  the  blue  color  disappears.  When 
completely  decolorized,  the  blue  color  may  return  after  a  little 
while  on  account  of  the  fact  that  the  last  traces  of  ferric  chloride 
are  reduced  very  slowly  by  hydriodic  acid  at  the  room  tempera- 
ture. To  hasten  this  decomposition,  heat  the  solution  to  50°,  or 
60°  at  the  most;  in  a  short  time  all  of  the  iron  will  be  reduced  to 
the  ferrous  condition.  Cool  the  flask  under  the  water  tap  and 
finish  tfre  titration  with  sodium  thiosulfate,  adding  a  little  more 
starch. 


172  CHEMICAL  ANALYSIS  OF  METALS 

To  the  amount  of  iron  thus  obtained,  a  correction  must  be 
added  corresponding  to  the  iron  remaining  in  the  aqueous  layer 
after  treatment  with  ether  and  also  for  that  remaining  with  the 
silica  and  obtained  as  ferric  oxide  after  the  volatilization  of  the 
silicon  fluoride.  Fuse  this  residue  with  a  little  sodium  carbonate 
and  dissolve  the  melt  in  a  little  dilute  hydrochloric  acid,  setting 
aside  the  solution.  In  the  aqueous  solution  obtained  after  the 
ether  separation,  precipitate  the  iron  as  basic  ferric  acetate,  by 
neutralizing  the  solution  with  ammonia,  making  acid  with  acetic 
acid  and  boiling  the  dilute  solution  with  3  g.  of  ammonium  aoetate. 
Dissolve  the  precipitate  in  hydrochloric  acid  and  add  the  solution 
to  the  iron  solution  obtained  from  the  silica  residue.  Evaporate 
off  the  excess  of  acid  and  carry  out  the  iodometric  determination 
of  the  iron. 

Instead  of  taking  the  ethereal  solution  of  ferric  chloride,  the 
solution  remaining  in  the  flask  after  the  evolution  method  for 
determining  sulfur  (p.  140)  may  be  used,  or  the  solution  obtained 
after  the  determination  of  copper  (p.  143).  After  the  removal  of 
the  copper,  which  is  always  necessary  when  appreciable  amounts 
of  copper  are  present  because  cupric  salts  react  with  potassium 
iodide  (cf.  p.  147),  concentrate  the  solution  by  evaporation  and 
carefully  oxidize  the  iron  by  adding  nitric  acid,  drop  by  drop,  or 
potassium  chlorate  (about  4  g.  for  10  g.  of  iron).  Evaporate  the 
solution  with  concentrated  hydrochloric  acid  to  remove  the  excess 
of  oxidizing  agent  and  carry  out  the  iodometric  determination 
in  an  aliquot  part  of  the  diluted  solution. 

Computation. — Assuming  that  n  c.c.  of  /-normal  sodium  thio- 
sulfate  were  used  in  titrating  the  iron  in  a  sample  representing 
s  g.  of  the  original  material,  then 

n  X/X  5.585 
per  cent  Fe  =  - 

s 

(B)  ZIMMERMANN-REINHARDT  METHOD 

Procedure. — In  an  aliquot  portion  of  the  original  solution,  ob- 
tained as  described  in  the  above  method,  determine  the  iron  by 
titration  with  permanganate  solution  after  reducing  with  stan- 
nous  chloride,  removing  the  excess  of  stannous  chloride  with 
mercuric  chloride  and  adding  manganous  sulfate  and  phosphoric 
acid  solution  exactly  as  described  on  p.  232  for  the  standardiza- 
tion of  a  ferric  chloride  solution. 


IRON  173 

2.  DETERMINATION  OF  IRON  IN  INSOLUBLE  MATERIALS 

Procedure. — Fuse  the  finely  pulverized  material  with  magnesia- 
sodium-carbonate  mixture  in  a  platinum  crucible  as  described  on 
p.  85.  Extract  the  melt  with  hot  water,  whereby  chromate, 
vanadate  and  other  substances  that  may  interfere  are  dissolved  in 
the  form  of  sodium  salts  of  the  corresponding  acids,  and  the  iron 
remains  behind  as  insoluble  ferric  oxide.  Wash  the  residue  thor- 
oughly and  determine  the  iron  by  either  of  the  above  volumetric 
methods. 

If  the  original  material  contained  no  appreciable  amount  of 
disturbing  substances  such  as  chromium,  vanadium  or  molybde- 
num, the  fusion  may  be  dissolved  at  once  in  dilute  hydrochloric 
acid  and  the  solution  used  for  the  titration. 

If  copper  is  present  to  an  appreciable  extent,  the  acid  solution 
should  be  saturated  with  hydrogen  sulfide,  the  copper  sulfide 
precipitate  filtered  off  and  the  iron  determined  in  the  filtrate  as 
described  on  p.  172. 

With  materials  rich  in  titanium,  the  fused  product  obtained 
after  ignition  with  magnesia-sodium-carbonate  mixture  should 
be  dissolved  directly  with  concentrated  hydrochloric  acid  (d.  1.2) 
or,  if  it  is  desired  to  remove  the  soluble  sodium  salts,  the  melt 
should  be  extracted  with  cold  and  not  hot  water  as  otherwise  it  is 
difficult  to  get  a  clear  solution  with  hydrochloric  acid.  Any 
pertitanic  acid  that  may  form  during  the  solution  of  the  melt  will 
be  reduced  during  the  subsequent  evaporation.1  In  this  case  the 
iodometric  method  should  be  used,  or  the  iron  should  be  reduced 
with  hydrogen  sulfide  (c/.  p.  239). 

Test  Analyses. — (a)  Determination  of  Iron  in  23  Per  Cent 
Nickel  Steel. — Using  samples  weighing  0.5  g.  and  carrying  out 
the  ether  separation  and  titration  with  sodium  thiosulfate,  the 
results  obtained  in  duplicate  experiments  were  75.6  and  75.6 
per  cent  Fe. 

(6)  Iron  in  Ferro-vanadium  with  25.7  Per  Cent  V. — Using 
4.0-g.  samples  and  one-twentieth  of  the  solution  for  the  final  titra- 
tion, the  values  obtained  were  71.5  and  71.6  per  cent  Fe. 

(c)  Iron  in  50  Per  Cent  Ferro-vanadium,  Rich  in  Carbon. — 
The  results  obtained  in  duplicate  experiments  using  the  ether 

1  KNECHT  and  HIBBERT,  J.  Soc.  Chem.  Ind.,  30,  396. 


174  CHEMICAL  ANALYSIS  OF  METALS 

separation  and  sodium  thiosulfate  titration  were  31.2  and  31.0  per 
cent  Fe. 

In  another  experiment  the  sample  was  fused  with  magnesia- 
sodium-carbonate  mixture  and  the  sodium  thiosulfate  titration 
showed  31.3  per  cent  Fe. 

(d)  Iron  Phosphide  with  24.9  Per  Cent  P.— Using  1.0  and  0.51- 
g.  samples  and  taking  three-tenths  of  the  solution  for  the  titration 
after  the  fusion  with  magnesia-sodium  carbonate,  the  results  ob- 
tained were  74.5  and  74.7  per  cent  Fe. 

(e)  Titanium  Metal,  63  Per  Cent  Pure. — Experiments  with  the 
fusion  method,  followed  by  sodium  thiosulfate  titration,  gave  the 
values  2.99  and  3.05  per  cent  Fe. 

ACCURACY   OF   THE  METHOD  AND  PERMISSIBLE  DEVIATION  IN 

THE  VALUES 

If  the  iodometric  method  for  the  determination  of  the  iron  is 
carefully  carried  out,  the  following  agreement  of  the  results  can  be 
obtained. 

IRON  CONTENT  PERMISSIBLE 

DEVIATION 

0.1  to      0.5  per  cent 0.02 

0.5  to      2.0  per  cent 0.03 

2.0  to    10.0  per  cent 0.05 

10.0  to    25.0  per  cent 0.10 

25.0  to    50.0  per  cent 0.15 

50.0  to  100.0  per  cent 0.20 


CHAPTER  X 
NICKEL 

Nickel,  in  traces  at  least,  is  a  very  common  constituent  of 
iron  and  steel.  It  is  rarely  present  much  in  excess  of  0 . 1  per  cent 
except  when  it  is  intentionally  added  in  special  steels. 

Three  methods  for  the  determination  of  this  element  will  be 
described,  the  dimethylglyoxime  method,  the  electrolytic  method, 
and  the  volumetric  method.  Of  these  methods  only  the  first 
mentioned  is  uninfluenced  by  the  presence  of  cobalt  which  almost 
invariably  accompanies  nickel.  Usually  the  cobalt  content  is  in 
the  neighborhood  of  1  per  cent  of  the  nickel  content;  the  results 
obtained  by  the  last  two  methods  should  be  correspondingly 
higher. 

1.  DETERMINATION  OF  NICKEL  BY  THE  DIMETHYLGLYOXIME 

METHOD 

Principle. — From  a  nearly  neutral  solution,  it  is  possible  to 
precipitate  nickel  quantitatively  by  the  addition  of  dimethyl- 
glyoxime1 in  alcoholic  solution.  The  method  was  first  used  by 
Tschugaeff2  for  the  qualitative  detection  of  traces  of  nickel  and 
was  perfected  by  Brunck  for  quantitative  work.3  Dimethyl- 
glyoxime, also  called  diacetyldioxime,  has  the  following  consti- 
tutional formula : 

CH3  -  C  -  C  -  CH3 

II        II 
HO  -  N      N  -  OH 

which  corresponds  to  the  empirical  formula,  C4H802N2.     One 

1  This  substance  was  expensive  until  a  demand  arose  for  it  as  reagent. 
In  1908  the  price  was  reduced  to  about  30  c.  a  gram  but  in  1911  it  cost 
only  about  4  c.  a  gram. 

2  Ber.,  38,  2520  (1905). 

3  Z.  angew.  chem.,  20,  1844  (1907). 

175 


176  CHEMICAL  ANALYSIS  OF  METALS 

atom  of  nickel  replaces  2  atoms  of  hydrogen  in  2  molecules 
of  dimethylglyoxime ;  the  reaction  may  be  written: 

CH3-C  -  C-CH3  CH3-C  -  C-CH3 

C 
HO-N       N-OH+ 

>Ni  +  2HC1 
HO-N       N-OH  HO-N-C 

.11         II  II 

CH3-C  -  C-CH3  CH3-C  -  C-CH3 

Dimethylglyoxime  Nickel  salt  of  dimethylglyoxime 

(C4H802N2)  (C8H14N404Ni) 

The  precipitation  may  be  accomplished  in  the  presence  of 
other  metals,  such  as  copper,  cobalt,  chromium,  iron,  manganese, 
tungsten  and  vanadium,  provided  a  sufficient  quantity  of  tartaric 
acid  is  present  to  prevent  any  precipitation  of  these  elements 
by  means  of  ammonia.  The  reagent  is  not  very  soluble  in  water 
and  for  this  reason  care  must  be  taken  not  to  use  too  large  an 
excess,  or  the  results  will  be  too  high. 

Requisite  Solutions. — Dimethylglyoxime  Solution. — Dissolve 
10  g.  of  dimethylglyoxime  in  1  liter  of  98  per  cent  alcohol  and 
filter  if  necessary.  Ten  cubic  centimeters  of  this  solution  will 
precipitate  approximately  0 . 025  g.  of  nickel. 

Hydrochloric  Acid,  approximately  6  normal  (cf.  p.  136). 

Procedure. — In  a  150-c.c.  beaker,  dissolve  1  g.  of  steel  in  20 
c.c.  of  6-normal  hydrochloric  acid  and  add  about  2  c.c.  of  concen- 
trated nitric  acid  to  oxidize  the  iron.  Filter  the  solution  and 
add  to  the  filtrate  6  g.  of  tartaric  acid  and  water  until  the  vol- 
ume is  about  300  c.c.  Add  ammonium  hydroxide  carefully 
until  the  solution  is  slightly  ammoniacal.  Often  a  yellow 
precipitate  of  basic  ferric  tartrate  is  obtained  when  the  solution 
is  neutral  but  this  precipitate  will  dissolve  upon  the  addition  of  a 
little  more  ammonia.  When  distinctly  ammoniacal  there  should 
be  no  precipitate  in  the  brown  solution.  If  a  precipitate  is 
present  it  indicates  too  little  tartaric  acid.  Make  the  solution 
barely  acid  with  hydrochloric  acid,  heat  it  nearly  to  boiling 
and  add  20  c.c.  of  the  alcoholic  solution  of  dimethylglyoxime, 
and  then  ammonia  until,  after  stirring  and  blowing  away  the 
vapors,  a  faint  odor  of  ammonia  can  be  detected  above  the  solu- 


NICKEL  177 

tion.  Any  nickel  present  will  be  precipitated  in  the  form  of 
fine  red  needles.1  After  allowing  the  solution  to  stand  a  little 
while,  add  10  c.c.  more  of  the  dimethylglyoxime  solution  to 
see  if  any  further  precipitation  takes  place.  If  this  is  the  case, 
it  may  be  necessary  to  add  still  more  of  the  reagent. 

Allow  the  solution  to  stand  in  a  warm  place  for  1  hr.  and  then 
allow  to  cool  for  about  %  hr. 

Meanwhile  prepare  a  Munroe  or  Gooch  crucible  (p.  81), 
place  it  in  a  platinum  or  nichrome  triangle  (Fig.  23),  heat  it  at 
120°  for  1  hr.,  cool  in  a  desiccator  and  weigh.  Filter  the  solution 
through  this  weighed  crucible,  using  gentle  suction.  Take  care 
to  keep  liquid  in  the  crucible  and  not  let 
the  crystals  get  packed  too  closely  on  the 
asbestos  felt,  as  this  interferes  with  the 
filtration.  Use  as  gentle  suction  as  will 
permit  rapid  filtration.  Wash  the  pre- 
cipitate with  hot  water  till  free  from  iron 
(8  to  12  times)  and  then  allow  it  to  drain. 
Place  the  crucible  in  the  platinum  or 
nichrome  triangle,  and  heat  in  a  hot 

closet  at  120°  for  at  least  J^  hr.  Cool  in  a  desiccator  and  weigh. 
Heat  again  in  the  hot  closet  to  see  if  the  weight  is  constant. 

To  clean  the  crucible,  pick  out  the  greater  part  of  the  precipi- 
tate without  interfering  with  the  asbestos  felt,  wash  with  hot 
dilute  hydrochloric  acid,  then  with  water  and  dry  at  120°,  after 
which  the  crucible  is  ready  for  use  again. 

Computation. — If  p  g.  of  nickel  precipitate  were  obtained 
in  the  analysis  of  s  g.  of  steel  then 

20.32  p 

per  cent  Ni  =  - 

8 

NOTES. — 1.  It  is  not  advisable  to  attempt  to  work  with  too  large  a  nickel 
precipitate.  The  weight  of  sample  should  be  regulated  so  that  the  quantity 
of  nickel  to  be  precipitated  shall  not  exceed  0.05  to  0.08  g.  Instead  of  weigh- 
ing out  a  very  small  sample  when  the  alloy  is  rich  in  nickel,  it  is  usually 
better,  for  the  sake  of  getting  a  good  average  sample,  to  dissolve  2  or  3  g. 
of  the  original  material  and  then  take  an  aliquot  part  for  the  final  precipi- 
tation. 

1  If  precipitation  takes  place  in  the  cold,  the  precipitate  is  of  a  slightly 
different  character  and  niters  less  readily. 
12  * 


178  CHEMICAL  ANALYSIS  OF  METALS 

Thus,  with  a  steel  containing  25  per  cent  of  nickel,  weigh  out  3  g.  of  the 
material,  dilute  the  solution  to  500  c.c.  in  a  calibrated  flask,  thoroughly 
mix  by  pouring  back  and  forth  several  times  into  a  dry  beaker,  and  then 
take  50  c.c.  (=  0.03  of  the  sample)  for  the  precipitation  with  dimethyl- 
glyoxime. 

2.  If  the  nickel  content  is  less  than  0.1  per  cent,  it  is  not  advisable  to 
attempt  to  carry  out  the  precipitation  of  the  nickel  in  the  presence  of  all 
the  iron.     In  such  cases,  carry  out  the  Rothe  ether  separation,  as  described 
on  p.  71  for  the  separation  of  iron  from  manganese,  and  then  proceed  as 
described  above  using  only  2  g.  of  tartaric  acid.     Or,  in  case  it  is  desired 
to  determine  other  elements  in  the  hydrochloric  acid  solution,  the  nickel 
may  be  precipitated  by  hydrogen  sulfide  in  acetic  acid  solution,  the  pre- 
cipitate  dissolved  in  a  little  aqua  regia,   the  free  chlorine  boiled  off,  the 
solution  diluted,  and  the  nickel  then  precipitated  with  dimethyl-glyoxime 
and  a  slight  excess  of  ammonia. 

3.  In  the  analysis  of  nickel-plated  iron  and  steel,  it  is  often  desired  to 
know  the  depth  of  the  nickel  coating.     In  such  cases,  dissolve  the  nickel 
coating  from  one  or  several  pieces,  the  surface  area  of  which  has  been  accu- 
rately measured,  in  cold  nitric  acid  (d.  1.42),  pour  off  the  nickel  solution 
into  a  second  beaker,  wash  the  metal  several  times  with  strong  nitric  acid, 
evaporate  off  the  excess  of  acid,  add  tartaric  acid  and  proceed  in  the  usual 
way  to  determine  the  nickel. 

Assuming  the  specific  gravity  of  nickel  to  be  8.9,  the  surface  of  the 
samples  examined  to  be  s  sq.  mm.,  and  the  weight  of  the  nickel  precipitate 
p  g.,  then  d,  the  thickness  of  the  nickel  coating,  is  given  by  the  equation: 

0.2032  p 

8.9s 

4.  Recovery  of  Dimethylglyoxime  from  Nickel  Precipitates. — Triturate  the 
precipitates  with  a  little  water  in  a  mortar,  rinse  the  paste  into  a  porcelain 
evaporating  dish  and  heat,  with  the  addition  of  a  little  potassium  cyanide, 
until  the  nickel  salt  dissolves  forming  a  reddish-yellow  solution.     Filter 
the  solution,  before  letting  it  stand  very  long,  through  a  plaited  filter  to 
remove  asbestos  fibers  and  other  insoluble  material.     Allow  the  solution  to 
cool  and  saturate  it  with  pure  carbon  dioxide  gas.     At  the  end  of  an  hour 
all  the  dimethylglyoxime  will  be  precipitated.     Filter  it  off  on  a  Biichner 
suction  funnel,  wash  with  cold  water,  dry  and  weigh.     Dissolve  the  dry 
powder  in  alcohol,  using  100  c.c.  for  each  gram  of  the  powder,  add  a  little 
bone  black,  heat  and  filter.     The  clear  solution  is  now  ready  for  use  as 
reagent. 

2.  DETERMINATION  OF  NICKEL  BY  ELECTROLYTIC  DEPOSITION 

Principle. — After  the  removal  of  the  greater  part  of  the  iron, 
preferably  by  the  Rothe  ether  separation,  and  the  precipitation 
of  the  copper  as  sulfide  from  acid  solution,  the  nickel  may  be 


NICKEL 


179 


deposited  electrolytically  from  an  ammoniacal  solution  containing 
ammonium  sulfate. 

Apparatus. — The  analysis  may  be  carried  out  with  a  platinum 
spiral  as  anode  and  a  platinum  plate  electrode  as  cathode,  but 
the  time  required  may  be  shortened  by  using  a  cylinder  of 
platinum  gauze  as  cathode,  which  permits  the  use  of  a  stronger 
current.  Stirring  the  electrolyte  is  also  helpful  and  this  can 
be  accomplished  very  satisfactorily  in  the  Frary  apparatus,1 
Fig.  24,  which  is  based  upon  the  principle  of  the  solenoid  and 
causes,  by  the  magnetic  influence  of  the  current  in  the  coil  of 
wire  in  the  apparatus,  the  rotation  of  the 
electrolyte  while  the  current  is  being 
passed  through  it.  The  platinum  gauze 
electrode  is  required  in  this  apparatus, 
as  it  allows  the  electrolyte  to  stream 
through  it.  The  movement  of  the  elec- 
trolyte is  not  satisfactory  when  a  solid 
electrode  is  used.  In  all  cases,  there  is 
less  danger  of  obtaining  spongy  deposits 
with  gauze  electrodes. 

Procedure. — Dissolve  3  to  5  g.  of  an 
ordinary  nickel  steel,  or  5  to  10  g.  of  a 

steel  with  low-nickel  content,  in  nitric  acid,  and  prepare  the 
solution  for  the  ether  separation  exactly  as  described  under 
Manganese,  p.  7 1.2 

After  the  removal  of  the  iron  by  the  ether,  evaporate  the 
solution  to  expel  the  dissolved  ether  and  precipitate  the  copper 
as  sulfide  according  to  p.  142.  Boil  the  filtrate  to  expel  hydrogen 
sulfide,  add  a  little  sulfuric  acid  and  evaporate  until  the  excess 
of  sulfuric  acid  is  expelled.  Treat  the  residue  with  sodium  hy- 
droxide and  sodium  peroxide  to  remove  chromium  as  described 
under  Manganese,  p.  76.3 

After  washing  out  the  sodium  chromate  and  other  sodium 

!Z.  Elektrochemie,  13,  308  (1907);  /.  Am.  Chem.  Soc.,  29,  1592  (1907). 

2  The  rapid  method  described  on  p.  88  may  be  used  for  the  removal  of  the 
silica. 

3  If  chromic  salts  are  present  during  the  electrolysis,  they  are  oxidized 
to  chromate  and  interfere  somewhat  with  the  deposition  of   nickel.     The 
addition  of  sodium  hypophosphite  to  the  bath  before  electrolysis  is  recom- 
mended when  chromium  is  present. 


FIG.  24. 


180  CHEMICAL  ANALYSIS  OF  METALS 

compounds,  dissolve  the  oxides  (chiefly  of  nickel,  cobalt,  man- 
ganese and  residual  iron)  by  heating  with  hydrochloric  acid 
(d.  1.10).  Dissolve  any  residue  in  the  platinum  dish  with 
a  crystal  of  oxalic  acid  and  a  little  sulfuric  acid,  and  add  the 
solution  to  that  already  obtained.  If  considerable  manganese 
is  present,  it  is  best  to  neutralize  the  solution  with  ammonia, 
acidify  it  slightly  with  acetic  acid  and  precipitate  the  nickel 
and  cobalt  with  hydrogen  sulfide.  Filter  off  the  sulfide  precipi- 
tate and  ignite  it  in  a  porcelain  crucible.  Dissolve  it  in  a  little 
aqua  regia  and  prepare  the  solution  for  electrolysis  as  described 
below.  Small  quantities  of  manganese  do  no  harm  and  in  such 
cases  it  is  unnecessary  to  precipitate  the  nickel  and  cobalt  as 
sulfides.  Add  a  slight  excess  of  sulfuric  acid  to  the  hydro- 
chloric acid  solution  and  evaporate  until  fumes  of  sulfuric  anhy- 
dride are  evolved.  Add  a  little  water  and  transfer  the  solution 
to  a  beaker  of  about  150-c.c.  capacity  which  fits  in  the  Frary 
apparatus.  Add  5  g.  of  solid  ammonium  sulfate  and  20  to 
30  c.c.  of  strong  ammonia  in  excess  of  the  quantity  required  to 
neutralize  the  solution.  Dilute  to  about  100  c.c.,  place  the 
beaker  in  the  Frary  apparatus  and  connect  the  electrodes,  as 
well  as  the  Frary  apparatus  itself,  with  the  source  of  electricity. 
With  a  current  of  5  amperes  passing  through  the  solution  and  a 
current  of  about  the  same  strength  through  the  coil,  the  nickel 
and  cobalt  should  all  be  deposited  in  less  than  J^  hr.  In  case  the 
gauze  electrode  is  used  with  a  stationary  electrolyte,  a  current 
of  0.7  to  1.0  ampere  should  cause  complete  deposition  in  1  hr. 
To  make  sure  that  the  electrolysis  is  complete,  add  a  little  water 
and  note  whether  any  deposition  of  metal  takes  place  on  the 
freshly  exposed  electrode  surface.  If  this  is  not  the  case,  with- 
draw a  few  drops  of  the  solution  by  means  of  a  pipette  and  add 
it  to  a  drop  of  ammonium  sulfide  on  a  porcelain  spot  plate. 
If  no  brown  precipitate  is  obtained,  the  deposition  is  complete. 
Disconnect  the  cathode,  quickly  withdraw  it  from  the  solu- 
tion and  at  once  transfer  it  to  a  beaker  containing  hot  water 
to  free  it  from  adhering  ammonium  salt.  Rinse  off  the  water 
with  alcohol,  dry  the  electrode  a  short  time  at  110°,  cool  and 
weigh. 

The  deposited  nickel  contains  any  cobalt  that  may  have  been 
present  in  the  sample. 


NICKEL  181 

TEST  ANALYSES 

(a)  Pure  Nickel  Solution. — Duplicate  electrolytic  determina- 
tions with  50-c.c.  portions  gave  the  values  0.1504  g.  and  0.1501 
g.  Ni.  Three  portions  of  the  same  solution  were  analyzed  by  the 
dimethylglyoxime  method  and  the  values  0.1502,  0.1505,  and 
0.1503  g.  Ni  were  obtained. 

Two  10-c.c.  portions  of  the  same  nickel  solution  (0.0301  g. 
Ni)  were  each  mixed  with  50  c.c.  of  pure  ferric  chloride  solution 
(4.8  g.  Fe)  and  to  one  portion  25  c.c.  of  manganous  chloride 
solution  (0.6  g.  Mn)  was  also  added.  The  nickel  was  then 
determined  in  each  solution  by  adding  tartaric  acid  and  dimethyl- 
glyoxime with  the  usual  precautions.  The  values  0.0305  g. 
and  0.0303  g.  Ni  were  obtained. 

(6)  Experiments  with  Nickel  Steel. — Using  a  sample  weigh- 
ing 0.5  g.,  the  dimethylglyoxime  method  gave  22.88  per  cent  Ni, 
and  with  0.2088  g.  of  the  steel  the  value  23.00  per  cent  Ni. 

Using  the  electrolytic  method  and  samples  weighing  respect- 
ively 1.000,  3.611,  and  3.861  g.,  the  values  23.40,  23.50,  and  23.46 
per  cent  Ni  were  obtained. 

The  difference  between  the  values  obtained  by  the  two  methods 
was  due  to  the  fact  that  the  steel  contained  about  0.51  per  cent 
of  cobalt. 

(c)  Determination  of  Nickel  by  the  Dimethylglyoxime  Method 
in  Various  Samples  of  Commercial  Steel. — Five  samples  of  steel 
and  cast  iron  with  nickel  content  ranging  from  0.01  to  5.05  per 
cent  were  analyzed  and  in  all  cases  duplicates  agreed  within  0.01 
per  cent. 

ACCURACY  OF  THE  VALUES  AND  PERMISSIBLE  DEVIATIONS 

Owing  to  the  fact  that  the  cobalt  content  of  different  steels 
varies  considerably,  it  often  happens  that  the  results  obtained 
by  the  dimethylglyoxime  method  are  considerably  lower  than 
those  obtained  by  electrolysis. 

If  it  is  desired  to  know  the  content  of  pure  nickel,  the  dimethyl- 
glyoxime method  is  the  better  method;  the  electrolytic  deposi- 
tion of  the  two  metals  followed  by  the  determination  of  the 
cobalt  is  a  much  more  tedious  operation. 

The  variations  in  the  weights  of  precipitate  in  duplicate  de- 


182  CHEMICAL  ANALYSIS  OF  METALS 

terminations  with  dimethyglyoxime  should  rarely  vary  more 
than  1  or  2  mg.  When  less  than  5  per  cent  of  nickel  is  present, 
the  determinations  should  agree  within  0.02  per  cent  and  within 
0.005  per  cent  if  less  than  1  per  cent  of  nickel  is  present. 

3.  VOLUMETRIC  DETERMINATION  OF  NICKEL  BY 
POTASSIUM  CYANIDE1 

Principle. — When  an  excess  of  ammonia  is  added  to  a  solution 
containing  nickel  ions,  a  pale  blue  nickel-ammonia  complex 
cation  is  formed.  Thus  with  nickel  chloride  the  reaction  may 
be  written: 

NiCl2  +  6NH3  =  [Ni(NH3)6]Cl2 

This  complex  nickel-ammonia  ion,  Ni(NH3)6++,  is  fairly  stable 
in  solutions  containing  ammonia,  but  on  adding  potassium  cya- 
nide a  much  more  stable  anion,  Ni(CN)4=,  is  formed 

[Ni(NH3)6]Cl2  +  4KCN  =  K2[Ni(CN)4]  +  6NH3  +  2KC1 

The  stability  of  this  nickelo-cyanide  ion  is  so  great,  and  its 
tendency  to  dissociate  into  simple  nickelous  cations  and  cyanide 
anions  is  so  slight,  that  potassium  cyanide  will  not  react  with 
insoluble  silver  iodide  until  all  the  nickel-ammonia  ions  have 
disappeared.  If,  then,  the  solution  originally  contained  some 
suspended  silver  iodide,  this  insoluble  compound  will  react  with 
potassium  cyanide,  after  all  the  nickel-ammonia  ions  have  dis- 
appeared, in  accordance  with  the  equation: 

Agl  +  2KCN  =  K[Ag(CN)2]  +  KI 

The  stability  of  this  argenticyanide  is  also  very  great.  The 
reason  why  the  potassium  cyanide  reacts  with  the  nickel-am- 
monia cations  rather  than  with  silver  can  be  traced  to  the  fact 
that  more  free  nickel  ions  are  present  in  a  slightly  ammoniacal 
solution  than  there  are  dissolved  silver  ions  in  the  liquid  which 
is  in  contact  with  precipitated  silver  iodide. 

1  cf.  CAMPBELL  and  ANDREWS,  J.  Am.  Chem.  Soc.,  17, 126  (1895);  MOORE, 
Chem.  News,  72,  92  (1895);  GOUTAL,  Z.  angew.  Chem.,  1898,  177;  BREARLEY 
and  JARVIS,  Chem.  News,  78,  177  and  190;  JOHNSON,  /.  Am.  Chem.  Soc.,  29, 
1201  (1907);  CAMPBELL  and  ARTHUR,  ibid.,  30,  1116  (1908);  GROSSMANN, 
Chem.  Ztg.,  32,  1223  (1908). 


NICKEL  183 

If,  after  all  the  nickel  and  silver  have  reacted  with  the  potas- 
sium cyanide  to  form  complex  anions,  a  little  silver  nitrate 
is  added,  it  reacts  with  the  potassium  iodide  to  form  a  precipi- 
tate of  silver  iodide. 

KI  +  AgN03  =  Agl  +  KNO3 

The  volumetric  determination  of  nickel  by  means  of  potassium 
cyanide  consists  in  adding  potassium  cyanide  to  a  nickel-am- 
monia solution  containing  a  known  quantity  of  silver  iodide  until 
the  precipitate  dissolves,  and  then  adding  just  enough  more  silver 
to  produce  a  turbidity  again.  By  deducting  the  volume  of 
potassium  cyanide  required  to  react  with  the  silver  from  the 
total  volume  used,  the  volume  of  potassium  cyanide  required  to 
react  with  the  nickel  is  known. 

The  method  can  be  carried  out  in  the  presence  of  most  of  the 
other  elements  of  the  ammonium  sulfide  group.  If  copper 
is  present  in  quantities  not  exceeding  0.4  per  cent,  the  cop- 
per will  replace  almost  exactly  three-quarters  of  its  weight  of 
nickel. 

When  cobalt  is  present,  the  solution  assumes  a  dark  color 
upon  the  addition  of  potassium  cyanide,  but  if  not  more  than 
one-tenth  of  1  per  cent  of  this  element  is  present  in  the  original 
sample,  the  titration  can  be  carried  out  successfully  and  the 
results  represent  the  amount  of  nickel  and  cobalt  present. 

The  determination  may  take  place  even  in  the  presence  of 
iron  if  a  considerable  quantity  of  citric  acid  or  tartaric  acid  is 
first  added  to  the  solution.  The  citric  or  tartaric  acid  prevents 
the  precipitation  of  the  iron  by  ammonia.  A  dark-colored  solu- 
tion results  and  the  end-point  cannot  be  distinguished  readily 
unless  a  large  excess  of  the  organic  acid  is  added.  This  will  also 
prevent  interference  by  chromium  present  as  chromic  salt. 

Necessary  Solutions. — Potassium  Cyanide  Solution. — A  con- 
venient strength  is  to  make  it  approximately  equivalent  to  tenth- 
normal  silver  nitrate.  Since  1  atom  of  silver  reacts  with  2 
molecules  of  potassium  cyanide,  it  follows  that  a  tenth-normal 
solution  of  potassium  cyanide  for  this  analysis  should  contain 
one-fifth  of  a  mole  dissolved  in  a  liter.  To  prepare  the  solution, 
therefore,  dissolve  13.5  g.  of  pure  potassium  cyanide  in  water, 
add  5  g.  of  potassium  hydroxide  dissolved  in  water,  and  dilute 


184  CHEMICAL  ANALYSIS  OF  METALS 

the  solution  to  1  liter.  Potassium  cyanide  containing  sulfide 
cannot  be  used;  it  forms  a  precipitate  of  silver  sulfide  with  the 
silver  added  and  silver  sulfide  is  not  dissolved  by  potassium 
cyanide. 

Tenth-normal  Silver  Nitrate  Solution. — Dissolve  exactly  8.495  g. 
of  pure  silver-nitrate  crystals,  that  have  been  powdered  and 
dried  J^  hr.  at  105°,  and  dilute  the  solution  to  exactly  1  liter  in 
a  calibrated  flask. 

Potassium  Iodide  Solution. — Dissolve  2  g.  of  potassium  iodide 
in  100  c.c.  of  water. 

To  standardize  the  potassium  cyanide  solution,  measure  out 
about  30  c.c.  of  it  from  a  burette,  dilute  to  about  100  c.c.,  add  5  c.c. 
of  potassium  iodide  solution,  and  titrate  with  silver  nitrate  until 
a  faint  permanent  opalescence  is  obtained.  The  opalescence 
should  be  so  slight  that  it  can  be  cleared  up  by  a  small  drop  of 
potassium  cyanide  solution.  The  reactions  that  take  place  are 
as  follows: 

2KCN  +  AgNO3  =  KAg(CN)2  +  KNO3 
KI  +  AgN03   =  Agl  +  KN03 

If  any  Agl  is  formed  before  the  first  reaction  is  finished  it  dis- 
solves, 

Agl  +  2KCN  =  KAg(CN)2  +  KI 

The  end-point  is  sharper  when  potassium  iodide  is  present. 
Without  it,  a  slight  excess  of  AgN03  would  react  with  the  com- 
plex cyanide  as  follows: 

KAg(CN)2  +  AgN03  =  KN03  +  2AgCN 

Procedure. — Dissolve  1  g.  of  steel  in  a  casserole  with  10  to 
50  c.c.  of  nitric  acid  (d.  1.2),  adding  a  little  hydrochloric  acid 
if  necessary.  After  the  steel  has  dissolved,  add  6  or  8  c.c.  of  con- 
centrated sulfuric  acid,  diluted  with  an  equal  volume  of  water, 
and  evaporate  until  fumes  of  sulfuric  acid  are  evolved.  Cool, 
add  30  to  40  c.c.  of  water  and  boil  the  contents  of  the  casserole 
until  all  the  ferric  sulfate  has  dissolved.  Transfer  the  solution  to 
a  400-c.c.  beaker,  dilute  to  about  300  c.c.  and  add  12  g.  of 
powdered  citric  acid,  or,  if  chromium  is  present,  add  twice  as 
much  citric  acid.  When  the  citric  acid  has  all  dissolved  make 
the  solution  faintly  but  distinctly  alkaline  with  ammonia. 


NICKEL  185 

As  the  ammonia  is  added  the  color  of  the  solution  changes. 
The  solution  turns  green,  then  yellow,  and  finally  assumes  a 
brownish  shade  when  the  ammonia  is  present  in  excess.  With 
the  large  amount  of  citric  acid  used,  the  color  is  not  such  a  deep 
red  as  when  only  a  little  is  present. 

To  the  cold  solution,  which  is  alkaline  to  litmus  but  does  not 
contain  a  large  excess  of  ammonia,  add  about  2  c.c.  of  the  potas- 
sium iodide  solution  and  enough  of  the  tenth-normal  silver 
nitrate  from  a  burette  to  produce  a  distinct  turbidity.  About 
0.5  c.c.  of  silver  nitrate  is  sufficient.  The  solution  is  now  ready 
for  titration  with  potassium  cyanide. 

Add  the  potassium  cyanide  solution,  while  stirring  constantly, 
until  the  precipitate  of  silver  iodide  disappears.  Then  finish  the 
titration  by  adding  just  enough  silver  nitrate  to  cause  the 
formation  of  a  very  slight  turbidity. 

Computation. — If  1  c.c.  of  potassium  cyanide  solution  is  equiva- 
lent to  t  c.c.  of  tenth-normal  silver  nitrate  solution,  and  n\  c.c. 
of  silver  nitrate  together  with  n2  c.c.  of  potassium  cyanide  are 
used  in  the  analysis  of  a  sample  of  steel  weighing  s  g.,  then 

(nzt  -  ni)  0.2934 
per  cent  Ni  =  - 

s 

NOTE. — The  temperature  of  the  solution  should  not  be  much 
above  20°  during  the  titration.  Too  large  an  excess  of  ammonia 
should  not  be  present  as  it  tends  to  impede  the  course  of  the 
reaction  by  making  the  nickel-ammonia  complex  more  stable  so 
that  it  is  not  decomposed  readily  by  the  potassium  cyanide. 

The  method  is  often  used  after  the  removal  of  the  iron  by  the 
ether  method.  It  is  then  easier  to  carry  out  the  titration.  The 
results  are  accurate. 

4.  DETERMINATION     OF     NICKEL     BY     THE     VOLUMETRIC- 
DIMETHYLGLYOXIME  METHOD1 

Principle. — The  nickel  is  precipitated  as  the  salt  of  dimethyl- 
glyoxime  and  the  precipitate  dissolved  in  nitric  acid.  The  organic 
matter  is  oxidized  by  treatment  with  ammonium  persulfate  and 
the  nickel  determined  by  potassium  cyanide  titration.  The 
method  is  recommended  for  routine  work. 

1  Am.  Soc.  Testing  Materials,  1915,  221. 


186  CHEMICAL  ANALYSIS  OF  METALS 

Solutions  Required — Hydrochloric  Acid,  approximately  6- 
normal. — (See  p.  136.) 

Dimethylglyoxime. — (See  p.  176.) 

Silver  Nitrate. — Dissolve  0.5  g.  of  silver  nitrate  in  1,000  c.c.  of 
distilled  water. 

Potassium  Iodide. — Dissolve  20  g.  of  the  solid  in  1,000  c.c. 
of  distilled  water. 

Standard  Potassium  Cyanide. — Dissolve  2.3  g.  of  the  salt  in 
1,000  c.c.  of  water.  To  standardize  the  potassium  cyanide 
solution,  first  titrate  about  30  c.c.  of  it  (accurately  measured) 
and  5  or  10  c.c.  of  potassium  iodide  solution  (approximately) 
with  silver  nitrate  solution  till  a  faint  permanent  opalescence  is 
obtained.  Then  standardize  the  solution  against  a  steel  of 
known  nickel  content,  e.g.  Bureau  of  Standards  Steel  No.  33, 
using  the  method  to  be  described.  In  every  titration  a  deduction 
must  be  made  for  the  potassium  cyanide  equivalent  to  the  silver 
nitrate  added.  For  convenience  it  is  well  to  adjust  the  concen- 
tration of  the  potassium  cyanide  solution  so  that  1  c.c.  =  0.0005 
g.  Ni  =  0.05  per  cent  in  the  analysis  of  a  1-g.  sample. 

Procedure. — Proceed  exactly  as  in  Method  1  till  the  precipitate 
of  dimethylglyoxime  salt  is  obtained  on  the  Gooch  filter.  Dis- 
solve the  precipitate  by  the  addition  of  10  to  20  c.c.  of  hot 
concentrated  nitric  acid,  added  drop  by  drop,  and  wash  the 
filter  five  times  using  suction.  To  the  solution  in  a  500-c.c. 
beaker,  add  3  g.  of  ammonium  persulfate  and  boil  for  5  min. 
Cool,  make  distinctly  ammoniacal,  add  exactly  10  c.c.  of  silver 
nitrate  (from  a  burette  or  pipette)  and  about  10  c.c.  of  potassium 
iodide  solution  from  a  graduate.  Titrate  with  potassium 
cyanide  to  a  faint  turbidity. 

6.  DETERMINATION    OF    NICKEL    BY    POTASSIUM    CYANIDE 
TITRATION  AFTER  ETHER  EXTRACTION 

Principle. — The  greater  part  of  the  iron  is  removed  by  the 
Rothe  Method  (p.  71)  and  the  remainder  by  precipitation 
with  ammonium  hydroxide,  the  copper  is  removed  by  precipi- 
tation as  sulfide  from  the  acid  solution  and  the  nickel  determined 
in  the  filtrate  by  potassium  cyanide  titration. 

Solutions  Required — Hydrochloric  Acid. — Mix  600  c.c.  of 
concentrated  acid,  d.,  1.2  with  400  c.c.  of  water. 


NICKEL  187 

Nitric  Acid. — Mix  1,000  c.c.  of  concentrated  acid,  d.  1.42 
with  1,200  c.c.  of  distilled  water. 

Potassium  Iodide,  Silver  Nitrate  and  Standard  Potassium 
Cyanide  solutions  as  in  the  preceding  method. 

Procedure. — In  a  150-c.c.  beaker,  dissolve  1  g.  of  the  steel  in 
20  c.c.  of  the  hydrochloric  acid  and  oxidize  the  iron  by  2  c.c. 
of  the  nitric  acid,  boiling  until  all  oxides  of  nitrogen  are  expelled. 
Cool  and  transfer  the  solution  to  a  250-c.c.  separatory  funnel 
rinsing  out  the  beaker  with  small  portions  of  the  acid.  Add 
50  c.c.  of  ether,  shake  for  5  min.,  let  stand  for  1  min.  and  then 
draw  off  the  lower  layer  of  solution  into  another  separatory 
funnel.  Add  10  c.c.  of  concentrated  hydrochloric  acid  to  the 
ethereal  solution  of  ferric  chloride  in  the  first  funnel,  cool,  shake 
and  withdraw  the  lower  liquid  into  the  second  funnel.  Then 
discard  the  ether  in  the  first  funnel,  or  preserve  it  to  recover  the 
ether  by  distillation  from  a  water-bath  away  from  any  flame. 

Shake  the  solution  in  the  second  separatory  funnel  with  another 
50-c.c.  portion  of  ether  and  withdraw  the  solution  into  a  150-c.c. 
beaker,  rinsing  the  ether,  as  before,  with  a  little  strong  hydro- 
chloric acid. 

Heat  the  solution  carefully  on  the  water  bath  to  expel  the  ether, 
add  0.2  g.  of  potassium  chlorate,  boil  until  the  chlorate  is  de- 
composed, dilute  to  100  c.c.  with  hot  water,  make  faintly  ammon- 
iacal  and  boil  for  5  min.  Filter  and  wash  with  hot  water. 
Rinse  the  ferric  hydroxide  precipitate  back  into  the  original 
beaker,  pour  a  little  hydrochloric  acid  through  the  filter-  to 
dissolve  the  adhering  precipitate  and  again  precipitate  with 
ammonium  hydroxide  of  which  a  little  is  also  poured  through  the 
filter.  Filter  off  the  ferric  hydroxide  and  wash  with  hot  water 
at  least  six  times. 

To  the  combined  filtrates  add  10  c.c.  of  concentrated  hydro- 
chloric acid  and  precipitate  the  copper  with  hydrogen  sulfide. 
Filter  and  wash  with  hot  water.  Boil  the  filtrate  to  expel 
hydrogen  sulfide  and  concentrate  the  solution  to  about  100  c.c. 
Cool,  make  distinctly  ammoniacal,  add  10  c.c.  each  of  standard 
silver  nitrate  and  potassium  iodide  solutions  and  titrate  with 
standard  potassium  cyanide  to  a  clear  solution. 


CHAPTER  XI 
MOLYBDENUM 

Molybdenum  is  seldom  present  as  impurity  in  iron  or  steel  but 
is  sometimes  added  intentionally.  Ferro-molybdenum,  chrome- 
molybdenum  and  metallic  molybdenum  are  used  in  the  prepara- 
tion of  special  steels. 

Molybdenum  is  interesting  to  the  chemist  because  it  has  so 
many  typical  reactions.  Compounds  representing  at  least  five 
different  states  of  oxidation  are  known,  corresponding  to  the 
oxides  MoO,  Mo2O3,  MoO2,  MoO3  and  Mo2O7.  The  first  three 
oxides  have  basic  properties  and  the  last  two  are  acid  anhydrides. 
The  analytical  chemist  often  refers  to  other  oxides,  such  as 
Moi2Oi9  or  Mo?.4O37,  but  it  is  probable  that  these  represent  merely 
a  partial  oxidation  of  trivalent  molybdenum  to  the  quadri- 
valent or  hexavalent  state.  Following  the  old  dualistic  nomen- 
clature, according  to  which  a  salt  was  regarded  as  an  oxide  of  a 
metal  combined  with  an  oxide  of  a  non-metal  (e.g.  K2SO4  was 
K2O-SO3  and  Na2CO3  was  Na2OCO2)  it  is  a  common,  though 
deplorable,  practice  for  analytical  chemists  to  call  the  oxide 
MoO3  molybdic  acid  and  to  speak  of  the  oxidation  of  molybdic 
sulfate  to  molybdic  acid  as  the  oxidation  of  Mo203  to  MoO3. 
To  make  this  point  clear,  let  us  compare  typical  oxidation  and 
reduction  reactions  of  molybdenum  with  those  of  iron. 

According  to  the  dualistic  nomenclature  the  reduction  of  ferric 
salt  in  acid  solution  by  means  of  zinc  is  expressed  as  follows: 

Zn  +  Fe203  =  ZnO  +  2FeO 

and  the  oxidation  back  to  ferric  salt  by  means  of  permanganate 
is  written 

lOFeO  +  Mn2O7  =  5Fe2O3  +  2MnO 

Now  we  know  that  there  is  absolutely  no  evidence  of  any  free 
ZnO,  FeO  or  Fe^O3  being  formed  at  any  time;  in  fact  these  oxides 
cannot  form  because  an  excess  of  free  acid  is  present  in  the  analy- 

188 


MOLYBDENUM  189 

tical  process.     The  modern,  and  somewhat  simpler  way  to  write 
these  reactions  is  as  follows : 

Zn  +  2Fe+++  -»  2Fe++  +  Zn++ 
5Fe++  +  MnO4~  +  8H+  ->  5Fe+++  +  Mn++  +  4H2O 

In  exactly  the  same  way,  the  oxidation  and  reduction  of  molyb- 
denum compounds  is  usually  written 

3Zn  +  2MoO3  =  3ZnO  +  Mo203 
5Mo2O3  +  3Mn207  =  6MnO  +  10MoO3 

but  these  equations  are  preferable  written  like  this: 

3Zn  +  2H2MoO4  +  12H+  4»  3Zn++  +  2Mo+++  +  8H2O 
5Mo+++  +  3Mn04~  +  3H2O  -»  5H2Mo04  +  3Mn++  +  6H+ 

The  best  known  compounds  of  molybdenum  are  molybdic 
acid  anhydride,  MoO3,  ammonium  molybdate,  (NH4)?MoO4 
(the  commercial  salt  corresponds  to  the  symbol  3(NH4)2 
Mo04-4H2Mo04)  and  ammonium  phosphomolybdate,  (NH4)3 
PO4-12MoO3. 

In  qualitative  schemes  of  analysis,  molybdenum  is  usually 
classed  with  arsenic,  antimony  and  tin  because  the  brown  sulfide, 
MoSa,  is  precipitated  by  means  of  hydrogen  sulfide  or  by  satur- 
ating an  ammonium  molybdate  solution  with  hydrogen  sulfide, 
forming  (NH4)2MoS4)  and  then  adding  acid: 

MoS4=  +  2H+  -»  MoS3  +  H2S  T 

Molybdic  acid  anhydride  is  very  slightly  soluble  in  water  but 
solutions  of  mineral  acids  dissolve  it  appreciably.  When  much 
molybdenum  is  present,  however,  a  little  of  the  acid  is  precipi- 
tated with  the  silica  upon  evaporating  the  acid  solution  fco  dryness. 
By  fusion  with  alkaline  fluxes,  molybdenum  compounds  are  con- 
verted into  water-soluble  alkali  molybdate,  and  by  fusion  with 
sodium  carbonate  and  sulfur,  sodium  thiomolybdate,  Na2MoS4, 
is  formed  which  is  soluble  in  water;  on  adding  acid  to  the  aqueous 
solution  of  sodium  thiomolybdate,  molybdenum  sulfide  is  pre- 
cipitated. 

In  several  methods  that  have  been  described  for  the  analysis 
of  iron  and  steel,  ferric  chloride  has  been  dissolved  out  of  the 
hydrochloric  acid  solution  by  shaking  with  ether;  molybdenum 
follows  the  iron  in  this  treatment. 


190  CHEMICAL  ANALYSIS  OF  METALS 

One  of  the  most  sensitive  tests  for  molybdenum  is  based  upon 
the  fact  that  when  a  little  molybdenum  compound  is  heated  with 
a  drop  of  sulfuric  acid  on  porcelain  until  nearly  all  the  sulfuric 
acid  has  been  driven  off,  the  cooled  mass  will  be  an  intense  blue 
(breathing  upon  it  sometimes  brings  out  the  color  but  water 
destroys  it).  This  test  can  be  obtained  with  less  than  0.1  mg. 
of  molybdenum  oxide,  but  it  is  not  always  obtained  with  an 
impure  product. 

From  neutral  solutions  of  alkali  molybdate,  mercurous  nitrate 
precipitates  white  mercurous  molybdate  and  lead  acetate  pre- 
cipitates white  lead  molybdate;  both  these  precipitates  are 
easily  dissolved  by  nitric  acid.  Potassium  ferrocyanide  produces 
a  brown  precipitate  or,  in  the  presence  of  oxalic  acetic  or  phos- 
phoric acids,  a  brown  coloration.  Sodium  phosphate  added  to 
a  nitric  acid  solution  of  a  molybdate  gives  a  yellow  precipitate  of 
ammonium  phosphomolybdate.  Potassium  thiocyanate,  KCNS, 
causes  no  reaction  with  molybdenum  when  added  to  a  molybdic 
acid  solution  containing  hydrochloric  acid  but  if  the  acid  solution 
is  then  treated  with  zinc  or  stannous  chloride,  a  blood-red 
coloration  is  obtained,  similar  to  that  obtained  with  ferric  ions 
and  potassium  thiocyanate;  this  is  also  a  sensitive  test  for 
molybdenum.  If  a  dry  molybdenum  compound  is  dissolved  in 
concentrated  ammonium  hydroxide  and  then  hydrogen  peroxide 
is  added,  the  solution  is  at  once  turned  pink  or  red ;  on  evaporating 
to  dryness  and  treating  the  residue  with  sulfuric  or  nitric  acid, 
yellow  permolybdic  acid,  HMoO4,  is  obtained. 

Zinc,  aluminium,  stannous  chloride  and  other  reducing  agents 
added  to  an  acid  solution  of  molybdate  causes  a  reduction  of  the 
molybdenum;  the  solution  is  colored  blue,  then  green  and  finally 
brown.  Sulfurous  acid  will  not  give  the  reaction  in  strongly  acid 
solution. 

1.  DETERMINATION  OF  MOLYBDENUM  BY  THE  SODIUM 
PEROXIDE  FUSION  METHOD 

Principle. — The  molybdenum  is  converted  into  water-soluble 
sodium  molybdate  by  fusion  with  sodium  peroxide  in  a  nickel  or 
iron  crucible.  In  the  aqueous  extract  of  the  melt,  the  sodium 
molybdate  is  converted  into  sodium  thiomolybdate  and  the 
latter  into  molybdenum  sulfide,  MoS3,  by  adding  acid. 


MOLYBDENUM  191 

Procedure. — If  the  material  can  be  pulverized,  fuse  1  to  2  g.  of 
the  powder  with  6  times  as  much  of  Rothe  magnesia-sodium 
carbonate  mixture  (1:2),  at  not  too  high  a  temperature,  and 
extract  the  ignited  product  with  hot  water  (p.  125).  Of  steel 
filings  or  drillings,  dissolve  2  to  3  g.  in  nitric  acid  (d.  1.2), 
destroy  the  nitrates  as  described  on  page  165,  and  fuse  the 
oxides  with  sodium  peroxide  in  a  nickel  crucible  at  a  relatively 
low  temperature. 

After  extracting  with  water,  filter  off  the  undissolved  oxides, 
wash  well  and  fuse  again  with  3  to  6  g.  pure  sodium  carbonate  in 
a  platinum  crucible.  Extract  the  product  of  this  fusion  with 
water  and  add  the  filtered  solution  to  that  previously  obtained. 

The  filtrates  now  contain  beside  all  the  molybdenum,  any 
vanadium,  tungsten,  phosphorus,  silicon,  etc.,  that  was  originally 
present.  If  the  molybdenum  content  is  considerable,  dilute  up 
to  the  mark  in  a  calibrated  flask  and  use  an  aliquot  part  of  the 
well-mixed  solution  for  the  further  analysis.  If  the  molybdenum 
content  is  small,  use  the  entire  solution. 

Neutralize  the  greater  part  of  the  alkali  with  dilute  sulfuric 
acid,  evaporate  the  solution  to  50  to  100  c.c.,  add  25  c.c.  of  strong 
ammonia,  and  saturate  the  solution  with  ammonium  sulfide. 
Then  acidify  with  dilute  sulfuric  acid  and  warm  the  solution 
while  passing  hydrogen  sulfide  gas  through  it.  In  this  way  there 
is  no  difficulty  in  precipitating  all  the  molybdenum  as  sulfide. 

If  tungsten  is  present,  add  tartaric  acid  to  the  solution  before 
making  it  acid.  This  prevents  the  precipitation  of  tungsten.1 

Filter  off  the  precipitate  of  molybdenum  sulfide  and  wash  the 
precipitate  with  very  dilute  sulfuric  acid  and  finally  with  water. 
Ignite  the  precipitate  with  the  filter  in  a  weighed  porcelain  cruci- 
ble at  as  low  a  temperature  as  possible.2 

Heat  the  crucible  at  first  with  a  very  low  flame  so  that  the  point 
of  the  flame  just  touches  the  crucible,  placing  this  flame  at  the 
front  of  the  crucible  until  all  the  moisture  is  expelled  and  then 
at  the  base  of  the  crucible,  so  that  escaping  hydrocarbons  will 
not  take  fire.  Turn  the  crucible  a  little  from  time  to  time  to 
hasten  the  decomposition  into  molybdenum  oxide,  MoO3. 
Finally,  when  all  but  a  little  of  the  carbon  has  been  consumed, 

1  FRIEDHEIM  and  MEYER,  Z.  anorg.  Chem.,  1,  76  (1892). 

2  Cf.  FRIEDHEIM  and  EULER,  Ber.,  28,  2061  (1895). 


192  CHEMICAL  ANALYSIS  OF  METALS 

dissolve  the  oxide  in  a  little  ammonia,  add  a  few  crystals  of  am- 
monium nitrate,  evaporate  carefully  to  dryness,  and  ignite  until 
all  the  ammonium  salts  are  volatilized.  If  necessary,  repeat 
this  treatment  till  all  the  carbon  is  consumed. 

If  vanadium  is  present,  the  molybdenum  trioxide  has  a  dark 
color.  After  weighing  the  oxides,  dissolve  them  in  a  little  caustic 
soda  solution  and  determine  the  vanadium  by  Method  2  or  3. 
pp.  210,  212.  Deduct  the  corresponding  amount  of  vanadium 
pentoxide  (1  c.c.  normal  solution  =  0.0091  g.  V2O5)  from  the 
weight  of  impure  molybdenum  oxide. 

If  arsenic  is  present,  it  may  be  removed  by  precipitating  the 
ammoniacal  solution  with  magnesia  mixture  before  precipitating 
the  molybdenum;  the  arsenic  is  precipitated  as  magnesium 
ammonium  arsenate,  which  on  ignition  is  changed  to  magnesium 
pyroarsenate,  Mg2As207. 

The  filtrate  from  the  hydrogen  sulfide  precipitation  will  have  a 
violet  or  bluish-green  color  if  chromium  and  vanadium  are  pres- 
ent. It  may  be  tested  again  with  hydrogen  sulfide  to  see  if  the 
precipitation  of  the  molybdenum  sulfide  was  complete. 

Pure  molybdenum  oxide  has  a  light  yellow  color  when  cold. 
On  adding  a  drop  of  sulfuric  acid  and  evaporating  off  the  excess 
acid,  a  beautiful  blue  color  is  obtained. 

Computation. — If  p  g.  of  pure  molybdenum  trioxide  were 
obtained  from  s  g.  of  steel,  then 

66.67  X  p 
per  cent  Mo  = 


2.  DETERMINATION    OF    MOLYBDENUM    BY    THE    ETHER 
EXTRACTION  METHOD  OF  BLAIR1 

Principle. — The  molybdenum  is  precipitated  in  acid  solution 
by  hydrogen  sulfide  under  pressure  and  the  molybdenum  sulfide 
thus  obtained  is  converted  into  molybdenum  trioxide,  MoO3, 
which  is  weighed. 

Procedure. — Carry  out  the  solution  of  the  sample  and  treat- 
ment with  ether  exactly  as  described  under  Manganese.  The 
molybdenum  will  be  found  in  the  etherial  solution  which  was 
discarded  in  the  manganese  determination.  (See  also  Sulfur.) 

1  J.  Am.  Chem.  Soc.,  30,  1228. 


MOLYBDENUM  193 

Evaporate  the  ether  solution  nearly  to  dryness,  add  10  c.c.  of 
concentrated  sulfuric  acid  and  again  evaporate  to  remove  the 
hydrochloric  acid.  Cool,  dissolve  in  about  100  c.c.  of  water  and 
reduce  the  ferric  salt  by  adding  ammonium  bisulfite.  Boil  off 
the  excess  of  sulfurous  acid  and  cool  the  solution.  Transfer  it  to 
a  200-c.c.  pressure  bottle,  saturate  with  hydrogen  sulfide  gas, 
stopper  the  bottle,  and  heat  on  the  water  bath  for  several  hours. 
Allow  the  solution  to  cool  slowly,  open  the  bottle,  and  filter  off 
the  molybdenum  sulfide.  Ignite  it  as  described  above  and  weigh 
the  pure  molybdenum  oxide,  MoO3. 

3.  VOLUMETRIC  DETERMINATION  OF  MOLYBDENUM 

Principle. — The  sample  is  dissolved  in  mineral  acids  and 
the  iron  separated  from  the  molybdenum  by  pouring  the  nearly 
neutral  solution  into  an  excess  of  sodium  hydroxide  solution. 
The  ferric  hydroxide  is  filtered  off  and  an  aliquot  part  of  the 
filtrate  is  saturated  with  hydrogen  sulfide;  any  resulting  precipi- 
tate is  filtered  off  and  the  molybdenum  is  precipitated  as  sulfide 
by  adding  acid  to  the  alkaline  sulfide  solution.  The  molybdenum 
sulfide  is  dissolved  in  acid,  reduced  to  the  trivalent  condition 
by  means  of  zinc,  oxidized  back  to  the  hexavalent  condition  by 
ferric  sulfate  solution  and  the  reduced  iron  determined  by 
titration  with  permanganate  (cf.  Phosphorus,  Method  6). 

Procedure. — Dissolve  2  g.  of  drillings  in  a  porcelain  casserole 
with  25  c.c.  of  concentrated  hydrochloric  acid  and  add  about 
2  c.c.  of  concentrated  nitric  acid  to  oxidize  the  iron  to  the  ferric 
state. 

If  a  precipitate  of  tungstic  acid  appears,  filter  it  off,  fuse  with 
a  little  sodium  peroxide  in  a  nickel  or  iron  crucible  and  examine 
for  molybdenum  as  in  Method  1.  If  a  precipitate  of  molybde- 
num sulfide  is  obtained,  ignite  and  weigh  it  as  oxide.  Compute 
the  per  cent  of  molybdenum  thus  obtained  and  add  it  to  that 
obtained  in  the  main  analysis,  remembering  that  the  sample 
weighed  2  g.  whereas  but  1  g.  is  used  in  the  volumetric  deter- 
mination. 

Nearly  neutralize  the  acid  solution  of  the  steel  with  2-normal 
sodium  hydroxide  and  heat  to  the  boiling  point.  Pour  the  hot 
solution  very  slowly  through  a  narrow-stem  funnel  into  70  c.c. 
of  2-normal  sodium  hydroxide  solution  contained  in  a  500-c.c. 

13 


194  CHEMICAL  ANALYSIS  OF  METALS 

calibrated  flask.  Cool,  make  up  to  the  mark  with  water  and 
mix  thoroughly.  Allow  the  precipitate  to  settle  and  filter 
through  a  dry  filter  until  half  the  solution  has  been  collected  in 
a  250-c.c.  calibrated  flask.  Nearly  neutralize  the  filtrate  with 
dilute  sulfuric  acid,  concentrate  to  about  100  c.c.,  add  25  c.c 
of  concentrated  ammonium  hydroxide  (d.  0.90),  and  saturate 
the  cold  solution  with  hydrogen  sulfide.  If  a  precipitate  appears, 
filter  it  off  and  wash  the  filter  with  hot  water.  If  tungsten  is 
likely  to  be  present,  add  2  g.  of  tartaric  acid  and  then  add  sulfuric 
acid  to  acid  reaction.  Heat  the  solution,  while  passing  hydro- 
gen sulfide  into  it,  and  filter  hot.  Wash  the  precipitate  of 
MoS3  with  very  dilute  sulfuric  acid  which  has  been  saturated 
with  hydrogen  sulfide. 

Dissolve  the  precipitated  molybdenum  sulfide  in  hot,  6-normal 
nitric  acid  catching  the  solution  in  a  porcelain  casserole.  Add 
10  c.c.  of  concentrated  sulfuric  acid  and  evaporate  till  fumes  of 
sulfuric  acid  are  evolved.  Cool,  wash  down  the  sides  of  the 
dish  with  water  and  again  evaporate  till  dense  fumes  are  evolved. 
This  second  evaporation  is  to  make  sure  that  every  trace  of 
nitric  acid  is  removed;  if  left  in  solution  it  will  be  reduced  in  the 
subsequent  precedure  and  cause  the  results  to  come  out  too 
high. 

Finally  dilute  to  about  100  c.c.  and  boil  with  granulated 
zinc  to  remove  any  copper.  Filter  through  an  alundum  or 
asbestos  filter  and  then  run  through  a  Jones  reductor  as  described 
on  page  108  allowing  the  reduced  solution  to  run  into  ferric  alum 
and  titrating  the  reduced  iron. 

Computation.  —  In  this  process  the  molybdenum  changes 
from  the  trivalent  to  the  hexavalent  condition  in  the  final  oxida- 
tion by  ferric  salt  and  an  equivalent  quantity  of  iron  is  reduced. 

1  c.c.  of  normal  permanganate  =  =  0.0320  g.  of  molybde- 


num. Or,  if  the  solution  of  permanganate  has  been  stand- 
ardized against  sodium  oxalate,  the  molybdenum  value  of  1  c.c. 
is  obtained  by  multiplying  the  sodium  oxalate  value  by 

°       =  0.4776.     According  to  the  above  directions,  only  one- 


half  the  original  weight  is  used  in  the  final  analysis. 


CHAPTER  XII 
TUNGSTEN 

Tungsten  is  not  found  very  often  in  steels.  It  is  never  present 
as  impurity  but  is  intentionally  added  in  special  alloy  steels  such 
as  high-speed  steels  in  quantities  up  to  20  per  cent  or  even  more. 

When  treated  with  an  oxidizing  acid,  metallic  tungsten  is 
converted  into  tungstic  acid,  or  its  anhydride,  W03.  All  of  the 
important  tungsten  minerals  are  salts  of  this  acid.  The  trioxide 
is  a  canary-yellow  powder,  insoluble  in  water  and  in  dilute  acids 
but  readily  dissolved  by  boiling  with  caustic  alkali  solutions  and 
less  readily  by  ammonium  hydroxide.  In  quantitative  analysis 
tungstic  acid  is  precipitated  in  much  the  same  way  that  silicic  acid 
is  obtained  or,  from  a  nearly  neutral  solution  of  an  alkali  tungstate, 
precipitates  of  mercurous  or  lead  tungstates  may  be  obtained,  both 
of  which  are  white.  Mercurous  and  ammonium  tungstates  are 
decomposed  by  gentle  ignition  and  tungstic  acid  anhydride,  WO3, 
is  left  behind.  This  is  itself  volatile  upon  strong  ignition. 

Reducing  agents  such  as  zinc  and  hydrochloric  acid  and 
stannous  chloride  give  characteristic  reactions  with  a  dilute 
solution  of  alkali  tungstate.  The  final  reduction  products  are 
blue  in  color,  probably  due  to  the  formation  of  WC15. 

By  boiling  with  dilute  hydrochloric  acid,  all  tungsten  can  be 
precipitated  as  the  trioxide  provided  no  colloidal  solution  is 
formed.  Alkali  salts,  however,  render  the  complete  deposition 
of  tungsten  trioxide  difficult.  The  precipitation  of  tungstic 
acid  anhydride  can  be  hastened  and  the  interfering  effects  of 
certain  dissolved  salts  lessened  by  means  of  a  solution  of  cin- 
chonine  hydrochloride. 

1.  DETERMINATION  OF  TUNGSTEN  AS  TRIOXIDE  BY  PRECIPITA- 
TION FROM  AN  ACID  SOLUTION  CONTAINING 
C1NCHON1NE  HYDROCHLORIDE1 

Principle. — The  tungsten  in  the  steel  is  oxidized  to  tungstic 
acid  by  treatment  with  concentrated  nitric  and  hydrochloric 

1  C.  M.  JOHNSON  (Rapid  Methods  for  the  Chemical  Analysis  of  Special 
Steels)  has  recommended  the  use  of  cinchonine  hydrochloride  solution  to 

195 


196  CHEMICAL  ANALYSIS  OF  METALS 

acids  and  the  precipitation  of  the  tungstic  acid  is  rendered 
complete  by  the  addition  of  cinchonine  hydrochloride.  After 
filtering  off  the  precipitate  it  is  purified  by  dissolving  it  in 
ammonium  hydroxide  and  reprecipitating  it  by  the  addition  of 
acid.  The  precipitate  is  ignited  at  a  low  temperature,  to  avoid 
volatilization  of  the  tungsten,  and  weighed  as  tungsten  trioxide, 
WO3. 

Solutions  Required. — Concentrated  Nitric  Acid  (d.  1.42); 
Concentrated  Hydrochloric  Acid  (d.  1.2);  and  Concentrated  Ammon- 
ium Hydroxide  (d.  0.90). 

Cinchonine  Hydrochloride. — Dissolve  125  g.  of  cinchonine 
in  500  c.c.  of  concentrated  hydrochloric  acid  and  dilute  with  an 
equal  volume  of  water. 

Cinchonine  Wash. — Use  10  c.c.  of  cinchonine  hydrochloride 
solution  to  1  liter  of  hot  water. 

Ammonia  Wash. — To  800  c.c.  of  water  add  200  c.c.  of  concen- 
trated ammonium  hydroxide  and  10  c.c.  of  concentrated  am- 
monium chloride. 

Filter-paper  Pulp. — Macerate  small  .pieces  of  ashless  filter 
paper  with  hot  water. 

Procedure. — Weigh  2  g.  of  steel  into  a  400-c.c.  beaker,  cover 
with  a  watch-glass  and  add  60  c.c.  of  a  mixture  of  equal  parts 
concentrated  nitric  and  hydrochloric  acids.  When  the  steel  is 
all  dissolved,  add  40  c.c.  of  concentrated  hydrochloric  acid  and 
20  c.c.  of  concentrated  nitric  acid  and  evaporate  the  solution  to 
a  volume  of  10  or  15  c.c.  Stir  the  residue  when  adding  the 
fresh  acid  and  break  up  any  crust  that  may  form  during  the 
evaporation. 

hasten  the  precipitation  of  tungstic  acid  from  acid  solutions.  The  method 
given  here  was  recommended  by  J.  A.  Holliday  (chemist  for  the  Electro 
Metallurgical  Company  of  Niagara  Falls)  for  the  analysis  of  tungsten  ores. 
The  method  has  been  tested  out  at  the  Bureau  of  Standards  and  by  a  number 
of  other  chemists  and  it  has  been  found  to  give  accurate  results.  M.  C. 
Hawes,  working  as  a  student  at  the  Massachusetts  Institute  of  Technology, 
found  that  there  was  danger  of  losing  tungstic  anhydride  by  volatiliza- 
tion unless  care  was  taken  in  the  final  ignition  not  to  expose  the  contents  of 
the  crucible  to  the  full  heat  of  the  burner;  the  crucible  should  not  be  cov- 
ered. D.  Belcher,  in  1916,  also  found  it  easy  to  volatilize  tungstic  anhy- 
dride although  it  has  been  stated  repeatedly  that  the  full  heat  of  a  Bunsen 
burner  can  be  used. 


TUNGSTEN  197 

If,  by  accident,  the  contents  of  the  beaker  should  go  to  dryness, 
add  50  c.c.  of  hydrochloric  acid  and  again  reduce  to  small  volume. 

Dilute  the  solution  with  150  c.c.  of  hot  water,  add  5  c.c.  of 
cinchonine  hydrochloride  solution  and  digest  on  the  hot  plate, 
at  a  temperature  near  the  boiling  point,  for  30  min.  Allow  the 
precipitate  to  settle  and  decant  off  the  solution  through  an 
ashless  paper  filter  containing  filter-paper  pulp.  Wash  the 
tungstic  acid  residue  three  times  by  decantation  with  hot  "  cin- 
chonine wash"  solution.  Transfer  the  precipitate  to  the  filter 
and  continue  washing  until  the  ferric  chloride  is  all  removed. 

Rinse  the  precipitate  back  into  the  original  beaker  using  not 
more  than  25  c.c.  of  water.  Add  6  c.c.  of  concentrated  ammon- 
ium hydroxide  and  gently  heat  the  contents  of  the  covered  beaker 
for  about  10  min.  Wash  down  the  sides  of  the  beaker  with  warm 
" ammonia  wash"  solution,  stir,  and  filter  through  the  original 
filter.  Wash  the  filter  thoroughly  with  the  " ammonia  wash" 
solution  until  all  the  tungsten  is  in  the  filtrate  in  the  form  of 
ammonium  tungstate. 

Evaporate  the  ammoniacal  solution  until  all  the  free  ammonia 
has  been  expelled.  This  point  is  important  because  an  excess 
of  ammonium  salt  will  render  the  subsequent  precipitation  of 
the  tungsten  incomplete.  Then  add  20  c.c.  of  concentrated 
hydrochloric  acid  and  10  c.c.  of  concentrated  nitric  acid  and 
digest  at  80  to  90°  for  about  30  min.  Add  an  excess  of  filter- 
paper  pulp  and  filter  through  a  9-cm.  filter  paper.  Wash  thor- 
oughly with  hot  "cinchonine  wash  solution." 

Ignite  in  a  platinum  crucible  at  a  low-red  heat  until  all  the 
carbon  has  been  oxidized  and  then  for  not  more  than  1  min. 
longer.  The  full  heat  of  a  Tirrill  burner  will  cause  volatilization 
of  tungstic  acid. 

The  presence  of  the  paper  pulp  causes  the  precipitate  to  dry 
to  a  porous,  friable  mass  from  which  the  carbon  is  easily  removed 
by  ignition  at  a  low  temperature.  The  ignited  oxide  contains 
79.31  per  cent  of  tungsten. 

2.  DETERMINATION    OF    TUNGSTEN    BY    THE  DEISS   METHOD 

Principle. — On  treating  a  steel  containing  tungsten  with  an 
oxidizing  acid  solvent,  all  the  tungsten  is  converted  into  tungstic 
acid  anhydride,  W03.  The  precipitation  of  this  substance  may 


198  CHEMICAL  ANALYSIS  OF  METALS 

be  made  quantitative  from  hydrochloric  acid  solutions  provided 
precautions  are  taken  to  prevent  some  of  it  remaining  in  the 
colloidal  condition  as  hydrosole. 

Procedure. — If  the  material  is  low  in  tungsten  use  a  10-g. 
sample,  otherwise  use  5  g.  or  less.  Weigh  the  sample  into  a  porce- 
lain casserole  and  dissolve  it  in  dilute  nitric  acid  (d.  1.2)  using 
110  c.c.  for  a  10-g.  portion  and  60  c.c.  for  a  5-g.  portion.  The 
material  should  be  in  the  form  of  fine  turnings.  Steels  with  much 
tungsten  often  resist  the  action  of  nitric  acid,  but  in  most  cases 
they  may  be  dissolved  slowly  by  adding  a  few  drops  of  concen- 
trated hydrochloric  acid,  waiting  till  all  action  has  ceased,  and 
repeating  the  addition  of  hydrochloric  acid  from  time  to  time. 

Evaporate  the  solution  to  dryness  and  heat  the  residue  to  de- 
compose the  nitrates.  When  no  more  nitrous  fumes  are  evolved 
by  strongly  heating  the  residue,  cool  it  somewhat,  moisten  with 
concentrated  hydrochloric  acid  (d.  1.2)  and  heat  gently  with 
50  c.c.  of  hydrochloric  acid  (d.  1.12)  until  finally  all  the  ferric 
oxide  has  dissolved.  The  residue  of  silica  and  tungstic  acid 
anhydride  should  not  be  colored  red  with  ferric  oxide  after  this 
treatment  with  hydrochloric  acid.  Again  evaporate  the  solution 
to  dryness  on  the  water  bath  and  heat  the  residue  at  135°  till  no 
more  acid  vapors  are  evolved.  Then  moisten  the  residue  once 
more  with  concentrated  hydrochloric  acid  and  dissolve  all  the 
iron  by  heating  with  6-normal  hydrochloric  acid,  but  do  not 
continue  heating  after  all  the  basic  ferric  chloride  has  dissolved. 
Evaporate  off  the  excess  of  hydrochloric  acid,  continuing  the 
process  as  far  as  possible  without  causing  solid  to  separate  out;  in 
this  way  a  thick  sirup  is  obtained.  It  is  necessary  to  follow  these 
directions  carefully  in  order  to  make  the  precipitation  of  the 
tungsten  quantitative. 

Allow  the  thick  sirup  to  cool  and  then  dilute  with  an  equal 
volume  of  dilute  hydrochloric  acid  (1  part  cone,  acid  to  5  parts 
water),  stir  and  allow  to  stand  a  few  minutes.  Filter  off  the 
deposited  silica  and  tungsten  trioxide  through  an  ashless  filter. 
Rinse  the  precipitate  from  the  dish  to  the  filter  by  means  of  dilute 
hydrochloric  acid  from  a  wash  bottle.  Usually,  when  tung- 
sten is  present,  a  yellow  film  of  tungsten  trioxide  remains  adher- 
ing to  the  porcelain  dish.  After  washing  the  dish  and  filter  with 
dilute  hydrochloric  acid  till  free  from  iron,  rub  the  dish  with  a 


TUNGSTEN  199 

filter  paper  moistened  with  ammonia  water  and  add  the  paper  to 
the  contents  of  the  filter;  the  ammonia  dissolves  the  yellow  tung- 
sten trioxide  forming  ammonium  tungstate  which  is  converted 
back  to  the  oxide  upon  ignition.  Finally  rub  the  dish  with  a 
piece  of  filter  paper  moistened  with  alcohol. 

If  the  tungsten  content  is  high  the  residue  often  filters  badly. 
It  is  a  good  plan  in  such  cases  to  add,  before  filtering,  a  little 
filter  paper  pulp  prepared  by  shaking  small  pieces  of  filter  paper 
with  hot  water;  this  prevents  the  pores  of  the  filter  from  becoming 
immediately  clogged  with  fine  precipitate.  Traces  of  tungsten 
trioxide  may  pass  through  the  filter  and  sometimes  the  turbidity 
thus  produced  is  scarcely  noticeable.  In  all  cases,  therefore, 
evaporate  the  filtrate  in  a  250-c.c.  beaker  as  far  as  possible  without 
causing  solid  salts  to  deposit  and  allow  the  liquid  to  cool.  Then, 
if  any  tungsten  trioxide  has  passed  through  the  filter,  it  will  settle 
out  on  the  bottom  of  the  beaker  and  be  distinctly  visible.  To  re- 
cover such  a  precipitate,  dilute  as  before  and  filter  through  a  fresh 
filter. 

The  filtrate  may  now  be  used  for  the  determination  of  other 
elements  such  as  manganese,  nickel,  chromium,  phosphorus,  etc. 

Heat  the  filters  and  precipitates  at  a  low  temperature  till  all 
the  carbon  is  consumed  and  finally  ignite  to  a  constant  weight 
over  the  full  heat  of  the  Bunsen  or  Tirrill  burner.  The  crucible 
must  not  be  heated  over  the  blast  lamp  because  at  high  tempera- 
tures tungstic  acid  is  volatilized  slowly. 

After  weighing  the  precipitate  of  silica  and  tungsten  trioxide, 
moisten  it  with  about  5  drops  of  sulfuric  acid  (1 : 1)  and  add  about 
2  c.c.  of  hydrofluoric  acid.  Evaporate  as  far  as  possible  on  the 
water  bath,  or  preferably  in  an  air  bath,  and  then  heat  very  care- 
fully with  the  free  flame  until  the  sulfuric  acid  is  expelled. 
Finally  heat  strongly  with  the  same  burner  that  was  used  for 
heating  the  impure  tungsten  trioxide.  The  loss  in  weight 
corresponds  to  the  amount  of  silica,  SiO2,  present  and  from  this 
the  quantity  of  silicon  in  the  steel  can  be  computed.  The  residue 
in  the  crucible,  however,  cannot  be  regarded  as  pure  tungsten 
trioxide.  It  is  invariably  contaminated  with  a  little  ferric  oxide 
and  may  contain  some  mangano-manganic  oxide,  Mn3C>4,  chromic 
oxide,  Cr203,  titanium  dioxide,  TiO2,  and  possibly  traces  of 
vanadium  pentoxide,  V^Os,  or  molybdenum  trioxide,  Mo03.  To 


200  CHEMICAL  ANALYSIS  OF  METALS 

purify  the  precipitate,  fuse  it  with  about  six  times  as  much 
sodium  carbonate.  Extract  the  fused  mass  with  a  little  water, 
wash  the  crucible  and  its  cover  carefully,  and  filter  off  the 
insoluble  residue  upon  a  small  filter.  Wash  the  precipitate  thor- 
oughly with  hot  water  and  then  ignite  it  in  the  same  crucible, 
without  attempting  to  clean  it  after  washing  out  the  soluble 
sodium  salts.  The  residue  contains  all  the  iron  and  titanium 
that  contaminated  the  tungsten  trioxide;  in  most  cases  the 
weight  of  this  residue  subtracted  from  the  previous  weight  of 
impure  tungsten  trioxide  obtained  after  the  removal  of  the  silica 
will  give  the  weight  of  pure  tungsten  trioxide.  For  the  direct 
determination  of  the  tungsten,  the  sodium  tungstate  solution, 
which  may  be  contaminated  with  chromium  as  shown  by  a 
yellow  colored  solution,  is  treated  with  mercurous  nitrate  solution 
in  the  following  manner. 

Add  a  piece  of  litmus  paper  to  the  solution  in  a  300  to  400-c.c. 
beaker,  cover  the  beaker  with  a  watch  glass  to  prevent  loss  by 
effervescence,  and  carefully  neutralize  the  solution  with  dilute 
nitric  acid  (1  part  concentrated  acid  to  5  parts  of  water).  Expel 
all  the  carbonic  acid  from  the  solution  by  boiling  gently  and 
then  add  to  the  hot,  neutralized  solution  some  mercurous  nitrate 
reagent  (p.  159)  until  no  further  precipitation  is  produced.  Stir 
the  solution  and  continue  the  boiling  for  a  short  time.  Allow 
the  precipitate  to  settle  and  test  with  a  little  more  mercurous 
nitrate  to  see  if  the  precipitation  was  complete.  Again  heat  to 
boiling,  allow  the  precipitate  to  settle  and  add  2  or  3  drops 
(not  more)  of  6-normal  ammonia  (d.  0.96).  This  addition 
of  ammonia  serves  to  neutralize  the  acid  of  the  mercurous  nitrate 
solution  (cf.  p.  163).  If  the  ammonia  is  not  added  some  of  the 
tungsten  may  remain  dissolved  as  metatungstate.  On  the  other 
hand,  if  too  much  ammonia  is  added,  this  will  cause  some  of  the 
precipitate  to  dissolve.  Many  chemists,  therefore,  prefer  not 
to  use  ammonia  and  add  instead  a  paste  containing  precipi- 
tated mercuric  oxide  stirred  up  with  water.  Then,  by  heating 
the  solution  with  this  paste,  the  excess  of  acid  can  be  neutralized. 

The  addition  of  the  few  drops  of  ammonia  should  cause  the 

/NH2 

formation  of  a  black  precipitate,  Hg<^          +  Hg,  showing  that 

XN03 


TUNGSTEN  201 

an  excess  of  mercurous  ions  is  present  in  the  solution.  Stir  the 
solution  well  and  boil  for  a  short  time.  The  precipitate  should 
retain  its  gray  color  during  the  boiling;  if  it  becomes  yellow 
again  it  is  necessary  to  add  a  little  more  ammonia  and  treat  as 
before. 

Allow  the  precipitate  to  settle  and  then  decant  the  clear  solu- 
tion through  an  ashless  filter.  When  all  the  clear  solution  has 
been  poured  through  the  filter,  cover  the  precipitate  with  hot 
water  and  add  a  few  c.c.  of  mercurous  nitrate  solution.  Boil 
a  short  time  and  again  decant  the  solution  through  the  filter. 
Continue  this  treatment  once  or  twice  more  in  order  to  remove 
all  the  soluble  alkali  salts.  Then  transfer  the  precipitate  to  the 
filter  and  wash  a  few  times  with  hot  water. 

The  precipitate  adhering  to  the  sides  of  the  beaker  can  usually 
be  removed  by  rubbing  it  with  a  moist  piece  of  filter  paper;  in 
case  it  has  dried  to  the  sides  of  the  beaker  and  is  hard  to  remove, 
use  a  filter  moistened  with  a  little  nitric  acid.  Place  the  filter 
paper  used  for  wiping  out  the  beaker  in  a  weighed  platinum 
crucible  and  burn  this  paper  by  itself,  allowing  the  air  to  enter 
the  crucible  freely.  Then  add  the  main  precipitate  while  still 
moist  on  the  filter  and  ignite  carefully  under  a  good  hood.  This 
ignition  may  take  place  without  danger  in  a  platinum  crucible 
provided  plenty  of  air  is  allowed  to  enter  the  crucible. 

After  the  filter  paper  is  all  consumed,  ignite  the  contents  of 
the  crucible  to  constant  weight  over  a  Bunsen  burner. 

If  the  solution  is  colorless  before  the  addition  of  the  mercurous 
nitrate  solution,  there  is  no  chromium  present  and  the  contents 
of  the  crucible  usually  consists  of  practically  pure  tungsten 
trioxide  of  light  yellow  color.  A  green  coloration  may  be  caused 
by  the  presence  of  a  little  alkali  or  of  a  trace  of  molybdenum 
trioxide. 

If  the  solution  was  yellow  before  the  addition  of  the  mercurous 
nitrate  solution,  chromium  is  present  and  the  ignited  tungsten 
trioxide  contains  chromium  and  has  a  greenish-gray  color. 

As  the  tungsten  was  originally  precipitated  from  strongly 
acid  solution,  it  seldom  happens  that  much  chromium  is  present 
at  this  stage  of  the  analysis.  After  weighing  the  impure  tungsten 
trioxide,  the  chromium  may  be  determined  by  fusing  the  residue 
with  sodium  carbonate,  dissolving  the  melt  in  water,  acidifying 


202  CHEMICAL  ANALYSIS  OF  METALS 

with  hydrochloric  acid  and  treating  with  potassium  iodide  and 
sodium  thiosulfate  solution  (p.  161)  or  the  residue  in  the  crucible 
may  be  fused  with  the  potassium  acid  tartrate  mixture  (p.  164) 
and  the  sodium  tungstate,  now  free  from  chromium,  washed  out 
with  water.  The  weight  of  chromic  oxide,  Cr203,  obtained  by 
computation  from  the  volume  of  sodium  thiosulfate  used,  or  by 
direct  weighing  of  the  residue  after  the  potassium  acid  tartrate 
fusion,  deducted  from  the  weight  of  impure  tungsten  trioxide, 
gives  the  weight  of  the  pure  substance.  The  uncolored  filtrate 
from  the  potassium  acid  tartrate  fusion  may  be  used  for  the 
direct  precipitation  of  the  tungsten  or,  in  special  cases,  for  the 
determination  of  vanadium  and  molybdenum. 

Computation. — If  p  represents  the  weight  of  pure  tungsten 
trioxide  obtained  in  the  analysis  of  s  g.  of  material  then 

per  cent  W  =-79.31 


3.  DETERMINATION  OF  TUNGSTEN  BY  THE  SODIUM-PEROXIDE- 
FUSION  METHOD* 

Principle. — If  a  mixture  of  ferric  oxide  and  tungstic  acid  anhy- 
dride is  fused  with  sodium  peroxide,  the  latter  is  converted  into 
soluble  sodium  tungstate  and  may  be  separated  from  the  ferric 
oxide  by  extracting  the  melt  with  water.  The  tungsten  may  be 
precipitated  by  means  of  mercurous  nitrate  but  the  mercurous 
tungstate  will  be  contaminated  by  mercurous  phosphate,  chro- 
mate,  vanadate  and  molybdate  to  the  extent  that  phosphorus, 
chromium,  vanadium  and  molybdenum  are  present  in  the  origi- 
nal material;  a  little  silica  is  also  likely  to  be  carried  down.  The 
precipitate,  therefore,  must  undergo  further  treatment  in  order 
to  obtain  pure  tungsten  trioxide. 

Procedure. — Weigh  out  2  g.  of  tungsten  steel  containing  about 
5  per  cent  tungsten,  or  1  g.  of  a  steel  richer  in  tungsten,  into  a 
small  porcelain  casserole.  Cover  the  casserole  with  a  watch- 
glass  and  treat  the  steel  with  30  c.c.  of  nitric  acid  (d.  1.2).  When 
the  steel  is  dissolved,  evaporate  the  solution  to  dryness  and  heat 
the  residue,  keeping  the  dish  covered  with  a  watch-glass,  until 

1  HINRICHSEN,  Mitt.  Kgl  Materialpriifungsamt,  26,  308  (1907)  or  Stahl 
u.  Eisen,  27,  1418  (1907). 


TUNGSTEN  203 

no  more  nitrous  fumes  are  evolved.  The  oxides  then  become 
detached,  for  the  most  part,  from  the  sides  of  the  dish. 

Transfer  the  oxides  as  completely  as  possible  to  an  agate  mortar 
and  mix  them  with  six  or  eight  times  as  much  pure  sodium 
peroxide.  Add  the  mixture  to  a  nickel  crucible.  Sprinkle  a 
little  more  sodium  peroxide  in  the  original  dish  and  add  this  to 
the  contents  of  the  crucible.  Dissolve  any  tungsten  in  the 
residue,  that  remains  adhering  to  the  dish,  by  heating  with  a  little 
caustic  soda  solution  and  add  this  solution  to  that  which  is 
eventually  obtained  from  the  sodium  peroxide  fusion. 

Heat  the  mixture  in  the  nickel  crucible  with  a  very  small  flame 
until  the  flux  is  melted  and  continue  the  heating  for  about  half  an 
hour,  heating  just  hot  enough  to  keep  the  sodium  peroxide  liquid. 
After  allowing  the  crucible  to  cool,  place  it  in  a  beaker  and  add 
just  enough  water  to  cover  the  crucible.  Heat  the  water  to 
hasten  the  solution  of  the  melt  and  when  all  is  dissolved,  remove 
the  crucible  and  wash  it  out  with  hot  water.  Dilute  the  solution 
to  about  200  c.c.  and,  if  it  appears  green  in  color  after  the  ferric 
hydroxide  has  settled  out,  add  a  little  sodium  peroxide  from  the 
blade  of  a  knife;  this  serves  to  reduce  sodium  mangariate  to  man- 
ganese dioxide.  Allow  the  precipitate  to  settle  completely  and 
decant  the  clear  solution  through  a  filter,  catching  the  filtrate 
in  a  250-c.c.  calibrated  flask.  Wash  the  precipitate  in  the  beaker 
by  pouring  dilute  sodium  carbonate  solution  (2  g.  per  100  c.c. 
water)  upon  it,  allow  the  precipitate  to  settle,  and  decant  the 
liquid  through  the  filter.  Repeat  the  washing  several  times  until 
certain  that  all  the  sodium  tungstate  has  been  dissolved.  Then 
cool  the  filtrate  to  room  temperature  and  dilute  to  the  mark. 
Mix  the  solution  thoroughly  and  take  an  aliquot  part  for  the 
further  analysis,  e.g.,  two-fifths.  Transfer  the  aliquot  part  of 
the  solution  to  a  beaker  of  about  350-c.c.  capacity  and  precipitate 
with  mercurous  nitrate  solution,  exactly  as  described  on  p.  200. 
Treat  the  precipitate  with  sulfuric  and  hydrofluoric  acids  to 
remove  the  silica  and  continue  the  purification  process  as  de- 
scribed on  p.  201. 

Instead  of  determining  the  chromium  in  the  same  sample,  it 
is  a  little  easier  to  take  another  aliquot  part  of  the  solution  and 
determine  the  chromium  in  it  according  to  p.  161.  By  multi- 
plying the  weight  of  chromium  thus  obtained  by  the  factor 


204  CHEMICAL  ANALYSIS  OF  METALS 

1.462,  the  corresponding  weight  of  chromic  oxide  is  obtained; 
deduct  this  from  the  weight  of  the  impure  tungsten  trioxide. 

If  vanadium  and  molybdenum  are  present,  these  elements 
must  be  determined  by  methods  to  be  described  in  the  sections 
of  this  book  which  immediately  follow.  Corresponding  quanti- 
ties of  VzOs  and  MoO3  must  be  deducted  from  the  weight  of 
impure  tungsten  trioxide. 

If  much  phosphorus  is  present  it  must  also  be  determined  and 
allowance  made.  As  a  rule,  however,  the  phosphorus  content 
of  tungsten  steel  is  not  over  0.03  per  cent  and  the  error  resulting 
from  neglecting  it  is  not  serious. 

4.  DETERMINATION  OF  TUNGSTEN  IN  MATERIALS  INSOLUBLE 

IN  ACID 

(Ferro-tungsten,  Metallic  Tungsten) 

Principle. — Iron  alloys  rich  in  tungsten  may  be  analyzed  by 
treatment  with  magnesia-sodium  carbonate  mixture  (p.  125) 
provided  the  metal  is  brittle  enough  to  be  powdered.  The 
tungsten  is  thereby  converted  to  sodium  tungstate  which  dissolves 
in  water. 

Procedure. — Mix  from  1  to  3  g.  of  the  finely  powdered  material 
in  an  agate  mortar  with  six  or  eight  times  as  much  of  Eschka 
mixture  and  heat  in  a  platinum  crucible  for  about  an  hour  over 
a  Meker  burner.  After  cooling,  extract  the  sintered  mass  in  a 
beaker  with  hot  water.  If  the  solution  is  colored  green  by  sodium 
manganate,  add  a  little  sodium  peroxide  and  heat  the  solution 
to  precipitate  the  manganese  as  dioxide.  Filter  off  the  sodium 
tungstate  after  allowing  the  precipitate  to  settle.  Wash  the 
residue  on  the  filter  with  hot  water,  then  transfer  it  to  the  same 
platinum  crucible  that  was  used  before,  smoke  off  the  filter  and 
heat  again  with  about  four  times  as  much  Eschka  mixture  as  the 
original  weight  of  the  material.  By  this  second  heating  of  an 
hour,  all  the  tungsten  is  converted  to  sodium  tungstate  unless 
the  material  was  too  coarse. 

The  well-washed  residue  may  be  used  for  the  determination  of 
iron  and  manganese. 

Dilute  the  combined  filtrates  in  a  500-c.c.  calibrated  flask  and 
determine  the  tungsten  in  an  aliquot  part  of  the  solution  by  the 


TUNGSTEN  205 

method  described  on  p.  196.  If  the  filtrate  obtained  after  igni- 
tion in  the  Eschka  mixture  is  yellow,  chromium  is  present;  in 
such  cases  determine  the  chromium  in  another  aliquot  part  of 
the  solution  (p.  161  et  seq.)  and  deduct  the  corresponding  weight 
of  chromic  oxide,  Cr2O3,  from  the  weight  of  impure  tungsten 
trioxide.  If  vanadium  and  molybdenum  are  present,  these  ele- 
ments must  also  be  determined  (pp.  212  and  193). 

The  method  just  described  can  be  used  for  the  determination 
of  tungsten  in  metallic  tungsten.  In  most  cases,  however,  it  is 
more  important  to  know  how  much  metallic  tungsten  an  alloy 
contains  rather  than  to  know  the  total  tungsten  content,  whether 
as  metal  or  oxide,  or  combined  with  other  non-metallic  elements. 
By  deducting  the  impurities  from  100,  the  percentage  of  metallic 
tungsten  can  be  found. 

To  determine  the  iron,  manganese,  lime,  calcium  and  magnesia, 
fuse  from  2  to  4  g.  of  the  finely  powdered  metal  with  six  times  as 
much  pure  sodium  carbonate,  placing  the  mixture  in  a  platinum 
crucible  which  already  contains  a  little  sodium  carbonate  on 
the  bottom.  Heat  the  fusion  mixture  an  hour  or  two  over  a 
Bunsen  burner  keeping  the  contents  of  the  crucible  just  below 
the  fusion  temperature.  Finally  raise  the  temperature  and 
heat  over  the  blast  lamp  for  a  short  time.  In  this  way  a  satis- 
factory fusion  can  be  made.  After  dissolving  the  melt  in  water, 
and  heating  with  a  little  sodium  peroxide,  the  residue  contains 
ferric  oxide,  manganese  dioxide,  nickel  oxide,  calcium  carbonate 
and  magnesium  carbonate  to  the  extent  that  these  elements  were 
present  in  the  metallic  tungsten.  Some  of  the  iron  usually  ad- 
heres to  the  sides  of  the  crucible;  dissolve  this  by  warming  with 
hydrochloric  acid.  All  these  substances  in  the  residue  are  de- 
termined in  the  usual  way.  Further  impurities  are  carbon, 
silicon,  oxygen  combined  with  iron  or  tungsten  (for  which  a 
corresponding  weight  of  ferric  oxide  or  tungsten  trioxide  is  de- 
ducted), phosphorus,  chromium,  vanadium,  molybdenum,  alu- 
minium, water-soluble  alkali  tungstate,  etc.  These  elements 
are  determined  as  described  in  the  corresponding  chapters  of 
this  book. 


CHAPTER  XIII 
VANADIUM 

Small  quantities  of  vanadium  are  often  present  in  cast  iron 
owing  to  the  presence  of  vanadium  in  the  iron  ore.  Vanadium  is 
oxidized  very  easily  and  for  that  reason  is  used,  like  aluminium 
and  titanium,  as  a  deoxidizing  agent  in  the  manufacture  of  steel. 
When  the  amount  of  vanadium  added  is  small,  the  greater  part  of 
it  passes  into  the  slag  so  that  the  finished  steel  is  often  greatly 
benefited  and  yet  does  not  contain  any  vanadium.  Special  steels, 
on  the  other  hand,  often  contain  vanadium  as  an  essential  part  of 
the  alloy. 

Vanadium,  like  nitrogen,  forms  five  oxides:  V2O,  V202,  V2O3, 
V2O4  and  V20s.  The  first  three  are  basic  anhydrides.  The  last 
two  oxides  represent  the  types  of  vanadium  compounds  usually 
encountered  in  analytical  chemistry.  V2O4  is  the  anhydride  of 
hypovanadic  acid,  V2O4  (OH)  4,  which  is  an  amphoteric  hydroxide. 
V2O4  itself  is  a  blue  powder  which  dissolves  in  concentrated  min- 
eral acids  forming  blue  divanadyl  salts. 

V204  +  2H2S04  =  V2O2(SO4)2  +  2H2O 

If  the  solution  of  divanadyl  salt  is  neutralized  carefully,  the 
insoluble  hydroxide  is  formed  but  it  dissolves  readily  in  alkali 
solutions  forming  brown  solutions  containing  compounds  like 
Na2V2O6  and  Na2V4O9,  both  being  called  hypovanadates. 

V2Os  is  the  anhydride  of  vanadic  acid  which  is  similar  to  phos- 
phoric acid  in  its  chemical  properties,  although  only  slightly 
soluble  in  water.  Like  phosphoric  acid,  it  forms  ortho-salts, 
meta-salts  and  pyro-salts;  of  these  the  meta  compounds  are  the 
most  stable  and  the  ortho  ones  the  least  so.  Thus  an  aqueous 
solution  of  ortho  vanadate  is  hydrolzyed,  even  in  the  cold,  into 
the  pyro-salt: 

2Na3VO4  +  H2O<=»Na4V207  +  2NaOH 
and  on  boiling  the  meta-salt  is  formed: 

Na4V2O7  +  H2O^2NaVO3  +  2NaOH 
206 


VANADIUM  207 

The  meta-,  pyro-,  and  ortho-salts  of  the  alkalies  are  colorless 
or  pale  yellow  but  polyvanadates,  e.g.,  the  tetra-  and  hexa- 
vanadates,  are  a  deep  orange  or  red  in  color.  Thus  a  pale 
yellow  solution  of  a  vanadate  is  colored  orange  on  the  addition 
of  acid. 

Vanadium  also  forms  pervanadic  acid,  HVC>4,  when  hydrogen 
peroxide  is  added  to  an  acid  solution  of  a  vanadate.  This  is 
reddish-brown  in  color  and  can  be  detected  when  only  a  trace  of 
vanadic  acid  is  contained  in  the  solution.  By  heating  with  acid, 
the  pervanadic  acid  decomposes  into  vanadyl  salt. 

The  insoluble  compounds  of  vanadium  most  used  in  the  gravi- 
metric determination  of  this  element  are,  ammonium  metavana- 
date,  NH4VO3,  which  is  practically  insoluble  in  a  concentrated 
solution  of  ammonium  chloride;  lead  vanadate,  which  although 
practically  insoluble  in  water  is  much  more  soluble  in  dilute  nitric 
acid  than  is  lead  chromate,  so  that  vanadic  and  chromic  acids 
may  be  precipitated  together  or  the  latter  alone  precipitated  in 
the  presence  of  dilute  nitric  acid;  and  mercurous  vanadate, 
Hg2(VO3)2,  which  is  white  and  soluble  in  nitric  acid. 

In  the  qualitative  scheme  of  analysis,  vanadium  is  usually 
classed  with  molybdenum  in  the  arsenic-tin  group.  Hydrogen 
sulfide,  however,  will  not  give  a  precipitate  of  either  ¥284  or 
¥285  when  introduced  into  an  acid  solution  of  divanadyl  salt  or 
of  vanadic  acid;  the  latter  is  reduced  to  vanadyl  salt.  If  a 
strongly  ammoniacal  solution  of  a  vanadate  or  hypovanadate 
is  saturated  with  hydrogen  sulfide,  the  color  of  the  solution 
deepens  and  finally  assumes  a  characteristic  violet-red  shade 
owing  to  the  formation  of  soluble  thio vanadate;  on  adding  acid 
to  the  red  solution  a  black  precipitate  of  ¥285  and  ¥284  is  thrown 
down  but  the  precipitation  is  not  quantitative. 

Vanadic  acid  is  like  phosphoric  acid  with  regard  to  precipi- 
tation with  ferric  iron  and  aluminium.  Thus  in  the  qualitative 
scheme,  vanadium  may  be  precipitated  by  ammonium  hydroxide 
as  V2O2(OH)4  if  the  vanadium  is  in  the  quadrivalent  condition, 
or  it  may  be  precipitated  as  ferric  or  aluminium  vanadate  if 
these  elements  are  present  and  the  vanadium  is  quinquivalent. 

Reducing  agents  (concentrated  hydrochloric  acid,  sulfurous 
acid,  hydrogen  sulfide,  alcohol,  oxalic,  citric  and  tartaric  acids, 
sugar,  etc.)  reduce  acid  solutions  of  vanadic  acid  to  blue  divanadyl 


208  CHEMICAL  ANALYSIS  OF  METALS 

salts.     With  hydriodic  acid  the  reduction  goes  farther  and  a 
green  solution  of  trivalent  vanadic  salt  is  obtained. 

The  volumetric  methods  for  determining  vanadium,  and  these 
are  the  most  accurate  for  determining  small  quantities  of  this 
element,  usually  depend  upon  getting  the  vanadium  entirely  into 
the  quadrivalent  condition  and  measuring  the  volume  of  standard 
oxidizing  solution  necessary  to  convert  the  quadrivalent  vana- 
dium completely  into  the  quinquevalent  state.  Referred  to  the 
old  oxide  theory,  this  is  often  regarded  as  the  oxidation  of 
V2O4  into  V4O5.  In  reality,  the  reaction  represents  the  oxida- 
tion of  blue  divanadyl  salt  into  vanadic  acid,  H3V04,  or  meta- 
vanadic  acid,  HVO3.  According  to  this  conception  the  reduction 
and  oxidation  may  be  represented  by  the  following  equations: 

2HVO3  +  H2SO3  +  H2SO4-+V2O2(S04)2  +  3H20 
5V2O2(SO4)2  +  2KMnO4  +  12H2O-»2MnSO4  +  2KHSO4  + 

10HV03  +  6H2SO4 

or,  in  terms  of  the  electrolytic  dissociation  theory: 

2VO3~  +  SOs"  +  6H+-»V2O2++  +  SO4=  +  3H2O 
5V2O2+++  2Mn04~  +  12H2O->10VO8~  +  2Mn++  +  24H+ 

1.  DETERMINATION    OF    VANADIUM    BY    THE    PHOSPHO- 
MOLYBDATE  PRECIPITATION  METHOD1 

Principle. — In  this  method  the  vanadium  is  oxidized  to  vanadic 
acid  and  precipitated,  together  with  phosphoric  acid,  by  means  of 
ammonium  molybdate.  The  precipitate  is  filtered  off  and  dis- 
solved in  hot,  concentrated  sulf uric  acid.  In  the  sulf uric  acid  solu- 
tion, the  vanadic  acid  is  converted  into  pervanadic  acid  by  treat- 
ment with  hydrogen  peroxide  in  the  cold  and  the  pervanadic  acid 
upon  further  heating  is  decomposed  into  blue  divanadyl  salt.  The 
latter  is  titrated  with  permanganate  and  vanadic  acid  formed. 

Solutions  Required. — Nitric  acid. — Mix  1,000  c.c.  of  concen- 
trated nitric  acid  (d.  1.42)  with  1,200  c.c.  of  distilled  water. 

Strong  Potassium  Permanganate. — Dissolve  25  g.  in  1  liter  of 
water. 

Sodium  Bisulfite. — Dissolve  30  g.  of  solid  in  1  liter  of  water. 

1  Am.  Soc.  Testing  Materials,  1915,  243. 


VANADIUM  209 

Ammonium  Phosphate. — 50  g.  in  1  liter  of  water. 

Ammonium  Molybdate. — See  Phosphorus,  p.  93. 

Acid  Ammonium  Sulfate. — Pour  50  c.c.  of  concentrated 
sulfuric  acid  (sp.  gr.  1.84)  into  950  c.c.  of  distilled  water,  shake 
and  add  15  c.c.  of  concentrated  ammonium  hydroxide  (d. 
0.90).  Use  at  a  temperature  of  80°. 

Standard  Potassium  Permanganate. — Dissolve  0.35  g.  of 
potassium  permanganate  in  1,000  c.c.  of  water  and  standardize 
against  pure  sodium  oxalate  (p.  58).  Since  in  the  titration  an 
atom  of  vanadium  changes  only  one  in  valence,  1  c.c.  of  normal 
permanganate  =  0.051  g.  of  vanadium.  Since  1  c.c.  of  normal 
KMnO4  =  0.067  g.  of  pure  sodium  oxalate,  it  is  clear  that  the 
vanadium  value  can  be  obtained  by  multiplying  the  sodium 
oxalate  value  by  the  fraction  51/67  =  0.761.  Ad  just  the  solution 
for  convenience  so  that  1  c.c.  permanganate  =  0.001  g.  vana- 
dium =  0.04  per  cent  V  when  2.5  g.  of  steel  is  taken  for  analysis. 

Procedure. — Dissolve  2.5  g.  of  steel  in  a  300-c.c.  Erlenmeyer 
flask  with  50  c.c.  of  nitric  acid.  Heat,  and  while  boiling  add 
6  c.c.  of  the  strong  permanganate  solution,  continuing  to  heat 
until  manganese  dioxide  precipitates.  Dissolve  the  precipitate 
by  the  addition  of  small  portions  of  sodium  bisulfite  solution  and 
boil  until  the  solution  is  clear  and  free  from  oxides  of  nitrogen. 
Add  5  c.c.  of  ammonium  phosphate  solution  and  10  g.  of  ammo- 
nium nitrate,  heat  to  boiling,  remove  from  the  hot  plate  and  add 
immediately  50  c.c.  of  the  ammonium  molybdate  solution.  Let 
stand  1  min.,  then  shake  or  agitate  for  3  min.  Filter  the  super- 
natant solution  through  an  asbestos  filter,  washing  three  times 
with  hot  acid  ammonium  sulfate  solution  and  drain  by  suction. 
Then  place  the  flask  containing  the  larger  part  of  the  precipitate 
under  the  funnel  and  treat  the  asbestos  pad  with  successive 
portions  of  hot,  concentrated  sulfuric  acid  (d.  1.84).  Heat  the 
solution  in  the  flask  until  all  the  precipitate  is  dissolved,  add  a 
few  drops  of  nitric  acid  and  evaporate  until  copious  fumes  of 
sulfuric  acid  are  evolved.  Cool,  add  hydrogen  peroxide  in  small 
quantities,  shaking  after  each  addition,  until  the  solution  shows 
a  brown  color.  Replace  the  flask  on  the  hot  plate  and  heat  4 
or  5  min.  longer  and  the  solution  becomes  a  clear  green  or  blue, 
showing  divanadyl  salt. 

If  after  this  treatment  the  color  of  vanadyl  salt  is  not  obtained, 

14 


210  CHEMICAL  ANALYSIS  OF  METALS 

heat  again  till  fumes  of  sulfuric  acid  are  evolved,  to  remove 
traces  of  nitric  acid  which  interfere  with  the  reaction.  Then 
cool  and  treat  with  hydrogen  peroxide  as  before. 

Finally  cool  the  solution,  dilute  carefully  with  100  c.c.  of 
distilled  water,  heat  to  80°  and  titrate  with  permanganate  to  a 
permanent  pink. 

2.  DETERMINATION    OF   VANADIUM   BY   THE   BLAIR    METHOD1 

The  method  is  very  similar  to  that  recommended  by  J.  R. 
Cain  and  L.  F.  Witmer  when  working  at  the  U.  S.  Bureau  of 
Standards.  They  precipitated  vanadic  acid  with  mercurous 
nitrate2  instead  of  using  lead  acetate  and  accomplished  the 
reduction  of  the  vanadium  by  means  of  sulfurous  acid,  as 
indicated  on  p.  208. 

Principle. — The  vanadium  is  separated  from  the  iron  as  in  the 
previous  method  and  from  chromium  by  precipitation  with 
sodium  hydroxide.  The  vanadium  is  then  precipitated  in  acetic 
acid  solution  by  means  of  lead  acetate.  The  lead  vanadate  is 
dissolved  in  hot  hydrochloric  acid,  the  vanadium  reduced  to 
vanadyl  salt  by  boiling  with  hydrochloric  acid  and  the  vanadyl 
salt  is  oxidized  with  potassium  permanganate.  The  reactions 
may  be  expressed  as  follows: 

Pb3(V04)2  +  6HC1    =  3PbCl2  +  2H3VO4 
2H3VO4  +  6HC1    =  2VOC12  +  6H2O  +  C12 

VOC12  +  H2SO4  =  VOSO4  +  2HC1 

5VOSO4  +  KMn04  +  11H20  =  5H3VO4  +  KHSO4  +  MnSO4 

+3H2SO4 

1  BLAIR,  A.  A.,  J.  Am.  Chem.  Soc.,  30,  1228. 

2  For  routine  work,  the  American  Society  for  Testing  Materials  sanc- 
tions the  determination  of  vanadium  without  removal  of  chromium,  using 
a  blank  determination  with  Cr  added  equivalent  to  the  Cr  content  of  the 
steel.     In  this  case,  after  the  removal  of  ether  in  the  procedure  of  Blair, 
25  c.c.  of  concentrated  sulfuric  acid  are  added  and  the  solution  is  evaporated 
to  fumes.     After  cooling,  25  c.c.  of  water  and  a  slight  excess  of  strong  per- 
manganate solution  (p.  208)  are  added  and  the  solution  is  boiled.     Then 
15  c.c.  of  concentrated  hydrochloric  acid  are  added  and  the  solution  is 
again  evaporated  until  fumes  of  sulfuric  acid  are  obtained.     Finally,  after 
again  diluting  with  water,  the  vanadyl  salt  is  titrated  with  permanganate 
at  60°. 


VANADIUM  211 

Procedure. — Carry  out  the  ether  separation  exactly  as  de- 
scribed on  p.  73  and  remove  the  dissolved  ether  by  evaporat- 
ing on  the  water  bath.  Add  nitric  acid  in  excess  and  evaporate 
to  remove  the  hydrochloric  acid.  When  the  solution  is  almost 
sirupy,  add  20  c.c.  of  hot  water  and  heat  with  a  few  drops  of 
sulfurous  acid  solution  to  reduce  any  chromic  acid  that  may  have 
been  formed.  Boil  and  slowly  pour  the  hot  solution,  stirring 
vigorously,  into  a  boiling  solution  of  sodium  hydroxide  (100  g. 
NaOH  to  the  liter;  1  c.c.  of  this  solution  will  neutralize  about 
2.4  c.c.  of  nitric  acid,  d.  1.2).  Boil  the  solution  a  few  minutes, 
allow  the  precipitate  to  settle,  filter,  and  wash  the  precipitate 
until  it  is  free  from  alkali.  The  precipitate  contains  the  hydrox- 
ides of  chromium,  nickel  and  iron,  copper  and  manganese  while 
the  vanadium  remains  in  the  filtrate  as  sodium  vanadate..  To 
remove  traces  of  chromium  that  may  be  left  in  the  filtrate, 
slightly  acidify  with  dilute  nitric  acid,  make  alkaline  with  sodium 
hydroxide  and  boil  again.  If  any  more  precipitate  is  formed, 
filter,  and  make  the  filtrate  acid  with  acetic  acid.  Heat  the 
filtrate  to  boiling,  add  an  excess  of  lead  acetate  solution  (usually 
10  c.c.  is  sufficient)  and  boil  for  several  minutes.  Filter  off  the 
precipitate  of  yellow  lead  vanadate  and  wash  it  with  hot  water. 
Dissolve  the  precipitate  by  pouring  hot  dilute  hydrochloric 
acid  through  the  filter.1  Evaporate  nearly  to  dryness,  add  50  c.c. 
of  hydrochloric  .acid  (d.  1.2),  and  again  evaporate  nearly  to 
dryness.  Finally  add  10  c.c.  of  concentrated  sulfuric  acid  and 
evaporate  until  the  acid  fumes  freely.  Cool,  dilute  to  150  c.c., 
heat  to  between  60  and  70°,  and  titrate  slowly  with  dilute  per- 
manganate solution. 

Computation. — If  n  c.c.  of /-normal  permanganate  were  used  in 
titrating  the  vanadium  in  a  sample  weighing  s  g.,  then  as  on  p.  209, 

.  „       nX/X5.10 
per  cent  V  =  - 

NOTES. — Campagne*  has  shown  that  good  results  can  be  obtained  by  this 
reduction  with  hydrochloric  acid  when  not  more  than  0.1  g.  of  vanadium  is 

1  If  there  is  much  precipitate,  remove  the  lead  by  evaporating  to  dryness, 
moistening  the  residue  with  hydrochloric  acid,  and  treating  with  alcohol. 
Filter  off  the  lead  chloride  and  evaporate  off  the  alcohol;  the  vanadium 
will  then  be  present  entirely  as  vanadyl  salt. 

2  Ber.,  36,  3164. 


212  CHEMICAL  ANALYSIS  OF  METALS 

present.  Gooch  and  Stockey1  have  also  shown  that  the  reduction  by  means 
of  hydrochloric  acid  is  practically  complete.  Rosenheim2  and  Holver- 
scheidt,3  however,  have  claimed  that  the  results  are  a  little  low,  and  that  the 
reduction  by  means  of  sulfurous  acid  is  safer.  With  this  reagent  the  reduc- 
tion is  accomplished  by  boiling  the  solution,  which  contains  sulfuric  acid, 
while  passing  sulfur  dioxide  through  it  until  the  solution  appears  a  pure 
blue,  showing  that  the  vanadic  acid  has  been  reduced  to  vanadyl  salt. 
Continue  the  boiling  and  replace  the  stream  of  sulfur  dioxide  with  one  of 
carbon  dioxide,  until  the  vapors  when  led  into  a  dilute  solution  of  potassium 
permanganate  will  no  longer  decolorize  it.  Then  titrate  the  hot  solution 
with  permanganate. 

This  method  may  be  carried  out  after  a  previous  titration  with  perman- 
ganate, so  that  it  may  be  used  as  a  check  upon  the  other  method. 

Mliller  and  Diefenthaler,4  in  the  analysis  of  ferro-vanadium,  found  that 
the  reduction  by  means  of  hydrochloric  acid  alone  did  not  always  give  de- 
pendable results.  They  found  that  much  depended  upon  the  exact  manner 
in  which  the  evaporation  was  conducted  and  that  different  values  were 
obtained  after  evaporation  in  an  Erlenmeyer  flask  than  when  an  open 
porcelain  evaporating  dish  was  used.  They  regard  the  reduction  with 
sulfurous  acid  as  the  standard  method  but  find  that  nearly  as  good  results 
can  be  obtained  by  evaporating  with  hydrochloric  acid  and  alcohol.  The 
procedure  they  recommended  for  the  analysis  of  ferro-vanadium  is  as 
follows: 

Weigh  about  1  g.  of  the  finely  divided  alloy  into  a  covered  beaker  and 
dissolve  it  in  a  little  concentrated  nitric  acid.  Evaporate  to  remove  the 
excess  nitric  acid,  add  a  little  concentrated  hydrochloric  acid  and  evaporate 
nearly  to  dryness  to  change  the  ferric  nitrate  into  ferric  chloride.  Add 
20  c.c.  more  of  concentrated  hydrochloric  acid  and  50  c.c.  of  alcohol  and 
evaporate,  by  gently  boiling  the  solution,  to  about  5  c.c.  Rinse  the  solu- 
tion into  a  calibrated  flask  and  determine  iron  in  one  aliquot  part  and  the 
vanadium  in  another. 

Determine  the  iron  by  the  iodometric  method  given  on  p.  170.  The 
results  are  usually  about  0.5  per  cent  too  high. 

Determine  the  vanadium  by  titrating  the  cold  solution  with  perman- 
ganate, using  the  manganese  sulfate  reagent  as  in  the  determination  of 
iron  by  the  Zimmerman-Reinhardt  method  (p.  232). 

3.  DETERMINATION  OF  VANADIUM  BY  AN  IODOMETRIC  METHOD 

Principle. — Vanadium,  like  manganese  and  many  other  metals, 
can  be  separated  from  ferric  chloride  in  hydrochloric  acid  solution 
by  shaking  the  solution  with  ether.  If,  however,  the  separation 

1  Chem.  News,  87,  133;  Z.  anorg.  Chem.,  32,  456. 

2  Ann.,  251,  197. 

3  Inaug.  Diss.,  Berlin,  1890. 

4  Z.  anorg.  Chem.,  71,  243  (1911). 


VANADIUM  213 

is  carried  out  exactly  as  described  for  manganese,  it  sometimes 
happens  that  a  little  vanadium  follows  the  iron  into  the  ether; 
this  vanadium  may  be  removed  from  the  ether  solution  by 
shaking  with  hydrochloric  acid  (d.  1.1)  that  has  been  saturated 
with  ether,  and  adding  a  few  drops  of  hydrogen  peroxide,  which 
forms  pervanadic  acid,  insoluble  in  ether. 

The  vanadium  may  be  separated  from  manganese,  nickel,  etc., 
by  an  oxidizing  fusion  (cf.  p.  76)  and  from  chromium  by  heating 
with  potassium  acid  tartrate  mixture  (p.  164).  In  the  aqueous 
extract  the  vanadium  may  be  determined  iodometrically  by  the 
method  of  Holverscheit.1  The  vanadic  acid,  containing  quin- 
quevalent  vanadium,  is  reduced  by  the  action  of  hydrobromic 
acid  to  either  hypovanadic  acid  or  vanadyl  salt,  probably  the 
latter,  in  which  the  vanadium  is  quadrivalent.  The  reaction 
may  be  expressed  as  follows: 

2V++    +  2Br~  =  2V++++  Br2 
or, 

2HVO3  +  2KBr  +  6HC1  =  2VOC12  +  2KC1  +  Br2  +  4H2O 

The  bromine  is  distilled  into  potassium  iodide  solution  and  the 
liberated  iodine  is  titrated  with  standard  thiosulfate  solution. 
The  equation  shows  that  1  atom  of  vanadium  loses  one  valence 
charge  and  is  equivalent  to  1  atom  of  bromine;  it  follows,  there- 
fore, that  1  c.c.  of  normal  sodium  thiosulfate  solution  is  equivalent 
to  0.0510  g.  of  vanadium. 

Inasmuch  as  the  vanadium  content  of  iron  and  steel  is  usually 
very  low,  it  is  advisable  to  use  an  approximately  fiftieth-normal 
solution,  prepared  by  taking  100  c.c.  of  tenth-normal  sodium 
thiosulfate,  standardized  as  described  on  p.  63,  147  or  156, 
and  diluting  to  exactly  500  c.c.  in  a  calibrated  flask.  The  titer 
of  the  well-mixed  solution  is  then  one-fifth  of  the  original  solution. 

Necessary  Apparatus  and  Solutions. — The  Rothe  shaking 
apparatus  and  ether-hydrochloric  acid  solutions  are  described 
on  p.  71.  For  distilling  off  the  iodine  and  catching  the  vapors 
in  potassium  iodide  solution,  the  Bunsen  apparatus  shown  in 
Fig.  25  is  used. 

Procedure. — Weigh  out  10  to  15  g.  of  the  material  into  a  porce- 
lain evaporating  dish  and  dissolve  in  dilute  nitric  acid  (d.1.2). 

1  Dissertation,  Berlin,  1890. 


214  CHEMICAL  ANALYSIS  OF  METALS 

Remove  the  silica  by  Method  3  (p.  121)  or  the  determination 
may  be  hastened  as  described  on  p.  121.  In  the  nitrate  from 
the  silica,  remove  the  ferric  chloride  by  shaking  with  ether  as 
described  on  p.  88.  To  remove  traces  of  vanadium  from  the 
ethereal  solution  of  ferric  chloride,  shake  the  latter  three  or  four 
times  with  the  10-c.c.  portions  of  ether-hydrochloric  acid  (d. 
1.10)  and  3  to  5  drops  of  3  per  cent  hydrogen  peroxide  solution, 
instead  of  with  ether-hydrochloric  acid  alone. 

Ether  usually  contains  a  little  peroxide,  and  this  suffices,  when 
the  vanadium  content  is  low,  to  give  a  reddish-brown  coloration 
to  the  aqueous  solution  first  obtained  on  shaking  with  ether.  If 
more  vanadium  is  present  the  vanadium  solution  first  obtained  is 
bluish-green  or  blue.  If  much  vanadium  is  present  the  ether  solu- 
tion will  usually  contain  an  appreciable  quantity  of  vanadium; 
when  this  is  the  case,  dark  brown  flocks  will  be  noticed  on  adding 
the  hydrogen  peroxide  to  the  olive-green  ferric  chloride  solution 
in  ether. 

After  the  removal  of  the  iron,  treat  the  solution  exactly  as 
described  on  p.  75,  finally  fusing  with  sodium  hydroxide  and 
sodium  peroxide,  and  dissolving  the  fused  mass  in  water. 

Filter  off  the  oxides  of  manganese  and  nickel  and  boil  the  fil- 
trate, which  is  yellow  if  chromium  is  present,  to  decompose  the 
excess  of  peroxide.  Neutralize  the  solution  with  dilute  nitric  acid 
and  precipitate  the  vanadium  with  mercurous  nitrate  solution 
exactly  as  described  under  Chromium  (p.  162).  Test  the  color- 
less filtrate  with  more  mercurous  nitrate  solution  to  see  if  the  pre- 
cipitation was  complete.  If  no  more  precipitate  is  formed, 
acidify  the  filtrate  with  nitric  acid  and  add  a  few  drops  of  hydro- 
gen peroxide;  if  all  the  vanadium  was  precipitated  there  will  be 
no  brown  coloration  of  pervanadic  acid.  The  precipitate  con- 
tains all  the  vanadium  and  chromium  together  with  some  phos- 
phorus. After  filtering  and  washing  the  precipitate,  ignite  it  to- 
gether with  the  filter  in  a  platinum  crucible,  fuse  with  potassium 
acid  tartrate  mixture  (cf.  Chromium,  p.  164),  and  extract  the 
product  of  the  fusion  with  a  little  hot  water. 

If  considerable  residue  was  obtained  after  heating  the  mercu- 
rous salt,  it  is  advisable  to  fuse  this  last  residue  of  chromic  oxide 
with  potassium  acid  tartrate  again.  The  fusion  may  be  accom- 
plished in  the  same  way  as  before,  or  the  chromic  oxide  may  be 


VANADIUM 


215 


fused  with  pure  sodium  carbonate  and  then  enough  potassium 
acid  tartrate  added  to  reduce  all  the  chromium  to  chromic  oxide. 
Extract  the  fused  product  with  hot  water  and  add  the  solution 
to  that  previously  obtained.  Wash  the  residual  chromic  oxide 
and  carbon  with  hot  water  until  the  soluble  alkali  salts  are 
all  dissolved. 

Concentrate  the  aqueous  solution  of  the  sodium  vanadate  to 
about  35  c.c.  and  transfer  it  to  the  decomposition  flask  of  the 
Bunsen  apparatus  (Fig.  25),  washing  out  the  beaker  several 
times  with  a  little  water  and  keeping  the  total  volume  of  liquid  as 
small  as  possible. 

Neutralize  the  solution  in 
the  flask  by  the  cautious 
addition  of  concentrated 
hydrochloric  acid  (free  from 
chlorine)  and  add  about  30 
c.c.  of  the  concentrated  acid 
in  excess  to  the  solution 
which  is  now  yellow  in  color. 
Introduce  about  3  g.  of  pure 
potassium  bromide  and  at 
once  connect  the  apparatus 
as  shown  in  the  drawing, 
placing  a  concentrated  solu- 
tion of  pure  potassium  iodide  (from  5  to  10  g.  free  from  iodate)  in 
the  receiver.  Arrange  the  apparatus  so  that  the  receiver  can  be 
turned  in  the  clamp  to  let  air  escape  during  the  distillation.  The 
tube  which  leads  from  the  distilling  flask  to -the  iodine  solution 
should  have  an  opening  from  1  to  2  mm.  in  diameter. 

Gradually  heat  the  liquid  in  the  flask  to  boiling  and  allow  the 
air  to  escape,  from  time  to  time,  by  turning  the  receiver.  After 
the  distillation  begins,  shown  by  the  fact  that  the  vapors  are 
absorbed  with  a  hissing  noise,  continue  heating  for  about  10  min. 
longer.  The  yellow  solution  in  the  distilling  flask  changes  to 
green  and  finally  blue  when  all  the  quinquevalent  vanadium  has 
been  reduced  to  the  quadrivalent  condition.  Then,  before  taking 
the  flame  away,  detach  the  receiver  from  the  clamp  and  remove  it 
from  the  delivery  tubing;  after  this  the  flame  may  be  withdrawn 
without  danger  of  the  solution  sucking  back.  Cool  the  contents 


FIG.  25. 


216  CHEMICAL  ANALYSIS  OF  METALS 

of  the  receiver  under  running  water,  rinse  it  into  an  Erlenmeyer 
flask,  and  titrate  the  free  iodine  with  sodium  thiosulf ate  solution, 
adding  starch  solution  toward  the  last.  To  make  certain  that 
there  is  no  unchanged  vanadate  in  the  decomposition  flask,  fill 
the  receiver  with  fresh  potassium  iodide  solution  and  repeat  the 
distillation. 

Computation. — If  n  c.c.  of  /-normal  sodium  thiosulf  ate  solu- 
tion were  used  in  titrating  the  vanadium  in  a  simple  weighing  s 
g.,  then 

,  _.        nX/X5.10 
per  cent  V  —  - 

s 

4.  DETERMINATION  OF  VANADIUM  AFTER  A  FUSION 

Principle. — The  finely  powdered  material  is  fused  with  a  suit- 
able alkaline  flux,  the  alkali  vanadate  thus  formed  is  dissolved 
in  water,  and  then  determined  as  in  the  above  methods.  To 
make  sure  that  the  residue  insoluble  in  water  contains  no  vana- 
dium, it  is  advisable  to  fuse  it  a  second  time. 

If  it  is  impossible  to  reduce  the  original  material  to  a  powder,  it 
is  best  to  treat  first  with  nitric  acid,  evaporate  the  nitrates  to 
dryness,  convert  them  into  oxides  by  ignition,  and  then  carry  out 
the  fusion. 

Procedure. — Mix  1  to  2  g.  of  the  finely  powdered  material  in  an 
agate  mortar  with  six  times  its  weight  of  Rothe  magnesia-sodium 
carbonate  mixture  (1:2)  and  heat  the  mixture  in  a  platinum  cru- 
cible as  described  on  p.  125. 

With  samples  which  are  not  brittle  enough  to  powder,  dissolve 
2  to  3  g.  in  a  small  porcelain  dish  with  nitric  acid  (d.  1.2), 
evaporate  the  solution,  heat  to  decompose  the  nitrates,  and 
fuse  the  residue  in  a  nickel  crucible  with  12  to  18  g.  of  sodium 
peroxide  (cf.  p.  165). 

In  both  cases,  extract  the  product  of  the  fusion  with  water;  if 
the  solution  is  colored  green  by  manganate,  reduce  the  latter  to 
manganese  dioxide  by  adding  a  little  sodium  peroxide. 

Then  filter  off  the  insoluble  residue  through  an  ashless  filter, 
wash  it  thoroughly  with  hot  water,  and  ignite  the  filter  with  its 
contents  in  a  platinum  crucible.  Mix  the  residue  with  3  to  6  g. 
of  sodium  carbonate,  again  fuse  and  extract  with  hot  water, 
adding  the  solution  to  that  previously  obtained. 


VANADIUM  217 

The  combined  filtrates  contain  all  the  vanadium  as  sodium 
vanadate  in  the  presence  of  sodium  phosphate,  chromate,  tung- 
state,  etc.  Neutralize  the  solution  with  nitric  acid  and  treat  with 
mercurous  nitrate  solution  as  described  on  p.  162.1 

If  the  vanadium  content  is  high,  so  that  a  large  mercurous  pre- 
cipitate is  to  be  expected,  dilute  the  solution  in  a  calibrated  flask 
and  use  an  aliquot  part  for  the  treatment  with  mercurous  nitrate. 

Filter  off  the  precipitate,  ignite,  and  fuse  the  oxides  with 
sodium  carbonate  and  acid  potassium  tartrate  as  described  on 
p.  164.  Extract  the  fusion  with  water,  filter  off  the  chromic  oxide 
and  carbon,  and  concentrate  the  filtrate  to  a  small  volume.  Neu- 
tralize the  solution  with  hydrochloric  acid  and  distil  with  potas- 
sium bromide  as  described  on  p.  215. 

Or,  instead  of  determining  the  vanadium  iodometrically,  the 
aqueous  solution  which  has  been  freed  from  chromium  may  be 
evaporated  with  hydrochloric  acid  and  the  reduced  vanadyl  salt 
determined  by  titrating  with  permanganate  (cf.  p.  211). 

5.  GRAVIMETRIC  DETERMINATION  OF  VANADIUM  2 

Principle. — Ammonium  metavanadate,  NH4VO3,  is  insoluble 
in  a  cold,  saturated  solution  of  ammonium  chloride.  By  ignition, 
it  is  changed  into  vanadium  pentoxide,  ¥265. 

The  ammonium  chloride  method  of  precipitating  vanadium 
cannot  be  used  in  the  presence  of  tungstate.3  If  chromate  is 
present,  some  chromate  is  precipitated  with  the  vanadium  and 
some  vanadium  is  not  precipitated,  so  that  in  many  cases  the 
correct  value  is  obtained  by  compensation.  The  presence  of 
phosphate,  arsenate,  molybdate  or  sulfate  does  not  seriously 
interfere. 

Procedure. — If  tungsten  is  present  start  the  analysis  according 
to  Method  3,  dissolving  about  5  g.  of  the  material,  removing  the 
silica  and  tungsten  from  hydrochloric  acid  solution,  the  iron  by 
shaking  with  ether,  and  fusing  in  a  platinum  dish,  etc. 

1  If  no  chromium  is  present,  the  aqueous  solution  is  colorless.     In  such 
a  case,  the  vanadium  can  be  determined  directly  without  previous  precipi- 
tation with  mercurous  nitrate.     Acidify  the  solution  at  once  with  hydro- 
chloric acid  and  transfer  to  the  evolution  flask. 

2  cf.  GOOCH  and  GILBERT,  Z.  anorg.  Chem.,  32,  175  (1902);  CAMPAGNE,  E., 
Ber.,  1903,  3164. 

3  ROSENHEIM,  Z.  anorg.  Chem.,  32,  181  (1902). 


218  CHEMICAL  ANALYSIS  OF  METALS 

In  the  absence  of  tungsten,  Method  4  may  be  used  for  starting 
the  analysis. 

Ignite  the  mercurous  nitrate  precipitate,  obtained  by  either  of 
these  methods,  and  remove  the  chromium  by  the  sodium  carbon- 
ate and  potassium  acid  tartrate  fusion.  Neutralize  the  aqueous 
extract  of  the  fusion  with  nitric  acid  and  decolorize  the  yellow 
solution  by  adding  a  little  ammonia  and  heating.  Estimate  the 
approximate  volume  of  the  solution  and,  if  it  seems  advisable, 
concentrate  it  somewhat. 

To  the  cold  solution  add,  all  at  once,  2.5  g.  of  pure  ammo- 
nium chloride  for  each  10  c.c.  of  solution  and  stir  vigorously  to 
dissolve  the  salt.  The  solution  becomes  colder,  a  turbidity  forms, 
and  gradually  white  flocks  of  ammonium  metavanadate  are  pre- 
cipitated. When  this  procedure  is  followed  there  is  little  tend- 
ency for  the  precipitate  to  attach  itself  to  the  sides  of  the  beaker. 

Allow  the  solution  to  stand  at  least  8  hr.,  then  filter  and  wash 
the  precipitate  with  cold,  25  per  cent  ammonium  chloride 
solution.  Ignite  the  precipitate  in  a  platinum  crucible,  finally 
melting  the  vanadium  pentoxide. 

After  weighing  the  oxide,  V^Os,  boil  it  with  a  little  concentrated 
sodium  hydroxide  solution.  It  should  dissolve  in  the  alkali  with- 
out leaving  any  residue.  The  purity  of  the  precipitate  may 
be  tested  by  pouring  the  solution  into  the  Bunsen  apparatus, 
acidifying  and  distilling  with  potassium  bromide,  as  described 
on  p.  215. 

Computation. — If  p  g.  of  vanadium  pentoxide  were  obtained 
from  a  sample  weighing  s  g.,  then 

per  cent  V  =  56.04- 

Test  Analysis. — (a)  Experiments  with  Sodium  Vanadate  Solu- 
tion.— Fifty  cubic  centimeters  of  the  solution  were  treated  with 
mercurous  nitrate  solution  and  on  ignition  0.3051  g.  of  VzOz  were 
obtained. 

Ten  cubic  centimeters  of  the  solution  required  6.65  c.c.  of 
sodium  thiosulfate  solution;  according  to  this,  50  c.c.  =  0.3030  g. 
V205. 

When  using  25  and  50-c.c.  portions  of  the  solution,  the  results 
obtained  by  iodometric  titration  corresponded  in  each  case  to 
0.3034  g.  V206  in  50  c.c. 


VANADIUM  219 

Twenty-five  cubic  centimeters  of  solution  precipitated  with 
ammonium  chloride  gave  0.1528  g.  V205;  50  c.c.  of  solution 
would  contain,  therefore,  0.3056  g.  ¥205. 

The  ammonium  chloride  process  was  carried  out  with  25-c.c. 
portions  of  sodium  vanadate  solution  in  the  presence  of  1-g. 
portions  of  each  of  the  following  salts:  potassium  acetate,  sodium 
nitrate,  sodium  sulfate,  sodium  phosphate,  potassium  arsena.te, 
ammonium  molybdate,  potassium  chromate  and  sodium  tung- 
state.  With  each  of  the  first  five  salts  the  values  ranged  from 
0.1520  to  0.1528  g.  of  V2C>6,  which  agreed  satisfactorily  with 
the  theoretical  value,  0.1526  g.  V2O5.  With  ammonium  molyb- 
date, the  precipitation  of  the  vanadium  was  complete  but  the 
precipitate  contained  about  2  mg.  of  impurity.  With  the 
chromate  about  the  same  excess  weight  was  obtained  and  the 
filtrate  contained  a  little  vanadium.  In  the  presence  of  tungsten, 
the  precipitate  weighed  about  3  mg.  too  little  and  contained 
tungsten. 

(b)  Separation  of  Vanadium  and  Iron  by  the  Ether  Process. — 
Ten  cubic  centimeters  of  a  vanadium  solution,  prepared  by  dis- 
solving  vanadium   pentoxide   in   hydrochloric   acid,    contained 
0.2300  g.  V2O5. 

When  mixed  with  ferric  chloride  solution,  corresponding  to  3.2 
g.  of  metallic  iron,  the  ammonium  chloride  precipitate  yielded 
0.2304  g.  V2O5.  With  ferric  chloride  corresponding  to  6.5  g.  of 
iron,  the  value  was  0.2295  g.  V2O5. 

(c)  Determination  of  Vanadium  in  Different  Materials. — The 
analysis   of   a   cast   iron   by   the   ammonium   chloride   process, 
using  4-g.  samples,  gave  0.029  per  cent  and  0.025  per  cent  V. 

Another  specimen  of  cast  iron  was  analyzed  by  Method  la  and 
the  values  obtained  with  5-g.  samples  were  0.139  per  cent  and 
0.133  per  cent  V. 

An  alloy  steel  containing  tungsten,  chromium,  molybdenum 
and  vanadium  was  analyzed  by  Method  la  and  the  values  ob- 
tained with  5-g.  samples  were  2.14  and  2.17  per  cent  V. 


CHAPTER  XIV 
ALUMINIUM 

In  the  manufacture  of  ingot  iron  and  mild  steel,  aluminium 
is  often  added  for  the  purpose  of  deoxidizing  the  molten  metal. 
Aluminium  is  present  in  iron,  therefore,  chiefly  in  the  form  of  its 
oxide.  If  more  aluminium  is  added  than  is  necessary  to  com- 
bine with  all  the  oxygen,  then  some  of  it  will  remain  in  solid 
solution  with  iron.  At  the  present  time  there  is  no  absolutely 
dependable  analytical  test  to  determine  whether  the  small 
quantity  of  aluminium  usually  found  is  present  as  oxide  or  as 
metal.  Certain  special  alloys,  e.g.,  aluminium  steel,  are  certain 
to  contain  metallic  aluminium. 

Principle. — Aluminium,  like  manganese,  chromium,  nickel,  etc., 
can  be  separated  from  iron  by  the  Rothe  method  of  shaking  the 
chlorides  in  hydrochloric  acid  solution  with  ether.  In  determin- 
ing the  aluminium  by  precipitation  as  aluminium  hydroxide  from 
dilute  acetic  acid  solution,  it  is  necessary  to  bear  in  mind  that  the 
phosphorus  from  the  steel  is  likely  to  be  precipitated  at  the  same 
time  as  aluminium  phosphate;1  for  this  reason  it  is  advisable  to 
precipitate  the  aluminium  intentionally  as  aluminium  phosphate. 

Procedure.  — Weigh  from  5  to  10  g.  of  steel  into  a  porcelain  dish 
and  dissolve  it  in  60  to  120  c.c.  of  concentrated  hydrochloric  acid. 
Evaporate  the  solution  to  dryness  and  remove  the  silica  according 
to  Method  I,2  p.  115.  Avoid  dehydrating  the  silica  at  too  high 
a  temperature  on  account  of  the  danger  of  volatilizing  aluminium 
chloride;  there  will  be  no  loss  in  a  hot  closet  at  135°.  The 
deposited  silica  is  likely  to  retain  a  little  aluminium.3  After 
treating  the  silica  with  hydrofluoric  and  sulfuric  acids,  therefore, 
fuse  the  residue  with  a  little  sodium  carbonate  and  determine  the 
aluminium  as  hydroxide  or  as  phosphate  as  described  for  the  main 
determination . 

1  When  steel  is  dissolved  in  hydrochloric  acid,  some  of  the  phosphorus  is 
evolved  as  phosphine. 

2  Or  by  method  3  p.  121;  cf,  d,  p.  88. 

3  If  the  residue  contains  much  aluminium  this  indicates  that  it  was  origi- 
nally present  as  oxide. 

220 


ALUMINIUM  221 

Concentrate  the  filtrate  from  the  silica  by  evaporating  until  a 
crust  of  crystals  begins  to  separate  on  the  edges  of  the  solution; 
then  add,  to  the  hot  solution,  dilute  nitric  acid  (d.1.2)  in  small 
quantities  and  cover  the  dish  with  a  watch-glass.  When  the 
oxidation  of  the  iron  is  complete,  which  is  recognized  by  the  fact 
that  no  more  oxides  of  nitrogen  are  evolved  and  the  solution  in  the 
dish  becomes  transparent,1  remove  the  watch-glass  and  evaporate 
the  solution  to  dryness.  To  remove  any  remaining  nitric  acid, 
take  up  the  residue  with  concentrated  hydrochloric  acid  and 
evaporate  to  the  consistency  of  sirup.  Shake  the  solution  of  the 
chlorides  with  ether  in  the  usual  manner  (cf.  p.  73). 

Evaporate  the  aqueous  chloride  solution,  which  is  nearly  free 
from  iron,  to  remove  the  ether  and  dissolve  the  residue  in  a  little 
hydrochloric  acid.  Dilute  the  solution  until  it  contains  about  25 
c.c.  of  water  for  each  c.c.  of  hydrochloric  acid  (d.  1.12)  pres- 
ent, precipitate  the  copper  by  adding  a  little  hydrogen  sulfide 
water  to  the  hot  solution  and  filter  off  the  copper  sulfide. 

Add  a  few  c.c.  of  dilute  sulfuric  acid  to  the  filtrate  and  evapo- 
rate the  solution  in  a  porcelain  dish  until  fumes  of  sulfuric  acid 
are  evolved;  it  is  necessary  to  heat  over  a  free  flame  toward 
the  last.  The  reason  for  transforming  the  chlorides  into  sulfates 
is  because  the  aluminium  precipitate  filters  better  when  deposited 
from  a  sulfate  solution.  Dissolve  the  residue  of  sulfates  in 
water,  heating  till  all  is  dissolved,  and  dilute  to  about  100  c.c. 
in  a  200  to  250-c.c.  beaker.  Add  ammonia  until  the  solution  is 
alkaline  to  litmus  paper  and  at  once  redissolve  the  aluminium 
hydroxide  with  as  little  dilute  sulfuric  acid  as  possible.  A  little 
brown  oxide  of  manganese  usually  remains  undissolved;  take 
this  up  by  adding  about  1  c.c.  of  sulfurous  acid.  To  the  slightly 
acid  solution,  add  2  or  3  c.c.  of  neutral  ammonium  acetate  solu- 
tion (100  g.  in  500  c.c.  of  water);  the  solution  should  still  have  a 
slightly  acid  reaction. 

Heat  the  solution  to  boiling,  which  causes  all  the  aluminium 
to  precipitate  together  with  some  impurity.  After  allowing  the 
precipitate  to  settle,  filter  and  wash  the  precipitate  with  water 
containing  a  little  ammonium  acetate.  Finally  rinse  back  the 

1  When  the  nitric  acid  is  first  added,  a  dark  brown  compound  with  NO 
and  ferrous  salt  is  formed.  This  disappears  when  no  more  ferrous  salt  is 
present. 


222  CHEMICAL  ANALYSIS  OF  METALS 

precipitate  into  the  original  beaker  and  dissolve  it  in  as  little 
sulfuric  acid  as  possible,  heating  on  the  water  bath  to  aid  the 
solution.  Repeat  the  precipitation  with  ammonium  acetate 
and  filter  through  the  same  filter,  washing  as  before. 

The  filtrate  now  contains  all  the  nickel  and  manganese  and  the 
precipitate  consists  chiefly  of  aluminium  hydroxide  and  phos- 
phate. Rinse  the  precipitate  back  into  the  beaker,  dissolve  it 
once  more  in  dilute  sulfuric  acid,  avoiding  an  excess,  add  1  or  2 
c.c.  of  ammonium  phosphate  solution  (100  g.  in  500  c.c.  of  water) 
and  reprecipitate  the  aluminium  by  adding  a  very  slight  excess 
of  ammonia  to  the  boiling  hot  solution. 

After  the  precipitation  is  complete,  acidify  slightly  with  acetic 
acid,  heat  to  boiling,  filter  and  wash  the  precipitate  with  hot  water 
containing  a  little  ammonium  acetate.  Ignite  and  weigh  as  A1PO4. 

When  perfectly  pure,  the  aluminium  phosphate  is  white.  If 
small  amounts  of  chromium  are  present  in  the  original  metal,  it  is 
precipitated  as  chromic  phosphate  with  the  aluminium  phosphate 
and  the  precipitate  has  a  grayish  or  green  tint.  In  such  cases, 
fuse  the  ignited  precipitate  with  a  little  sodium  carbonate  and 
determine  the  chromic  acid  by  treating  the  acid  extract  of  the 
melt  with  potassium  iodide  and  titrating  the  iodine  set  free  with 
standard  thiosulfate  solution  (cf.  p.  161).  Compute  the  quantity 
of  chromic  phosphate  corresponding  to  this  titration  and  sub- 
tract it  from  the  weight  of  the  phosphate  precipitate  previously 
obtained. 

When  the  Rothe  separation  is  successfully  accomplished,  not 
more  than  1  or  2  mg.  of  iron  should  follow  the  aluminium 
into  the  aqueous  layer  obtained  in  the  treatment  with  ether. 
In  such  cases  the  aluminium  precipitate  is  not  contaminated 
with  iron,  which  is  in  the  ferrous  condition  owing  to  the  ad- 
dition of  sulfurous  acid.  If,  however,  the  first  precipitation  of 
hydroxides  obtained  in  the  above  procedure  is  plainly  contami- 
nated with  iron,  it  is  advisable  to  evaporate  the  sulfuric  acid  solu- 
tion to  dryness  in  a  platinum  dish,  heat  until  the  free  sulfuric  acid 
is  all  expelled,  and  fuse  with  a  little  caustic  soda  and  sodium 
peroxide,  as  described  under  Manganese,  p.  76.  Neutralize  the 
aqueous  extract  of  the  melt  with  sulfuric  acid,  remove  the  sodium 
salts  by  precipitating  the  aluminium  twice  with  ammonia,  and 
finally  precipitate  the  aluminium  phosphate  as  described  above. 


ALUMINIUM  223 

Computation.  —  If  a  sample  of  steel  weighing  s  g.  gives  p.  g. 
of  aluminum  phosphate,  then 

pXAlXlOO       22. 


cent  Al 


AlPO.Xs 


Test  Analysis.  —  (1)  Experiments  with  Aluminium  Chloride 
Solution.  —  Twenty  cubic  centimeters  of  an  aluminium  chloride 
solution  free  from  phosphoric  acid  gave,  in  two  experiments  by 
precipitation  with  ammonium  acetate  and  weighing  as  Al20s, 
the  values  0.0464  and  0.0465  g.  Al. 

The  same  quantities  of  solution  analyzed  by  precipitation  as 
A1PO4  gave  the  values  0.0475  and  0.0477  g.  Al. 

In  two  other  experiments,  in  which  ferric  chloride  equivalent 
to  5  g.  of  metallic  iron  was  added  in  each  case,  the  values  0.0491 
and  0.0475  g.  Al  were  obtained. 

2.  Analysis  of  Aluminium  Steel.  Sample  1.  —  Duplicate  deter- 
minations in  5-g.  samples  gave  the  values  0.23  and  0.25  per  cent 
Al.  The  silica  precipitate  contained  no  aluminium. 

Sample  2.  —  (a)  In  the  analysis  of  a  sample  weighing  5  g.,  a 
precipitate  of  aluminium  phosphate  weighing  0.0687  g.  was  ob- 
tained in  the  main  analysis.  This  precipitate  was  contaminated 
with  chromium  and  the  subsequent  titration  with  sodium  thio- 
sulfate  showed  0.0036  g.  of  CrPO4.  Subtracting  this  from  the 
original  weight  of  the  phosphate  precipitate,  the  value  0.292  per 
cent  Al  was  obtained. 

The  silica  precipitate  was  tested  for  aluminium  and  additional 
aluminium  amounting  to  0.033  per  cent  obtained,  making  the 
total  Al  content  =  0.33  per  cent. 

(6)  A  duplicate  determination  with  similar  results  gave  0.34  per 
cent  Al. 

ACCURACY  OF  ALUMINIUM  VALUES  AND  PERMISSIBLE 
DEVIATIONS 

The  values  reported  in  samples  containing  up  to  1  per  cent  Al 
should  be  accurate  to  within  0.05  per  cent,  provided  a  careful 
blank  is  made  with  the  same  quantities  of  reagents  as  used  in  a 
regular  analysis. 


CHAPTER  XV 
ARSENIC 

Arsenic  occurs  quite  commonly  in  iron  ores  and  for  this  reason 
there  is  likely  to  be  some  arsenic  in  most  samples  of  iron  and  steel; 
von  Reis  found  in  some  cases  as  much  as  0.08  per  cent  arsenic. 

Inasmuch  as  arsenic  tends  to  injure  the  metal,  the  knowledge 
of  the  arsenic  content  is  of  importance  in  judging  the  value  of  a 
given  material.  A  previous  chapter  has  shown  the  effect  of 
arsenic  on  the  determination  of  phosphorus  so  that  a  knowledge  of 
the  arsenic  content  is  of  importance  to  the  chemist  in  helping  him 
to  choose  a  suitable  method  for  that  determination. 

Principle. — When  iron  or  steel  is  dissolved  in  nitric  acid  the 
arsenic  is  converted  into  arsenic  acid.  On  evaporating  to  dryness 
and  decomposing  the  nitrates  all  the  arsenic  remains  in  the  residue 
as  arsenate. 

From  the  hydrochloric  acid  solution  of  the  residue  it  is  possible 
to  distil  off  arsenic  trichloride  after  reducing  the  iron  to  the  fer- 
rous state  by  means  of  a  suitable  reducing  agent.1  One  of  the 
most  satisfactory  reducing  agents  in  this  case  is  cuprous  chlo- 
ride. The  reduction  process  can  then  be  represented  by  the  ionic 
equation 

Fe+++  +  Cu+  =  Fe++  +  Cu++ 

Accordingly,  56  parts  by  weight  of  iron  require  99  parts  by 
weight  of  cuprous  chloride. 

Procedure. — Dissolve  10  to  12  g.  of  the  iron  or  steel  in  a500-c.c. 
round-bottomed  flask  by  the  gradual  addition  of  nitric  acid  (d. 
1.2),  and  heating  over  the  Bunsen  flame.  Evaporate  to  dry- 
ness  (cf.  p.  88)  and  heat  the  residue  until  no  more  nitrous  fumes 
are  evolved.  Cool  and  dissolve  the  residue  in  80  to  100  c.c.  of 
concentrated  hydrochloric  acid,  warming  very  gently  and  rotat- 
ing the  liquid  about  in  the  flask.  The  liquid  must  not  be  heated 
to  boiling  as  there  is  a  chance  of  some  arsenic  being  lost  thereby. 

1  Some  reducing  agents,  e.g.,  stannous  chloride  and  sodium  hypophos- 
phite,  reduce  a  part  of  the  arsenic  to  the  metallic  condition  and  others,  e.g., 
zinc  and  iron,  reduce  it  to  arsine,  AsHs.  Ferrous  salts  reduce  quinquevalent 
arsenic  to  the  trivalent  state. 

224 


ARSENIC 


225 


For  each  10  g.  of  sample,  add  18  g.  of  pure,  arsenic-free  cuprous 
chloride  to  the  distilling  flask,  Fig.  26,  pour  upon  it  the  hydro- 
chloric acid  solution  of  the  sample  and  wash  out  the  contents  of 
the  original  flask  with  hydrochloric  acid  (d.  1.12).  With  the 
apparatus  all  in  place,  heat  the  contents  of  the  distilling  flask 
to  boiling  and  catch  the  distillate  in  a 
500  to  600-c.c.  beaker.  When  only 
about  50  c.c.  of  liquid  remain  in  the  flask, 
stop  heating,  add  50  c.c.  of  concentrated 
hydrochloric  acid  (sp.  gr.  1.2)  and  care- 
fully distil  again.  These  two  distillations 
are  sufficient  to  volatilize  all  the  arsenic 
as  trichloride. 

Dilute  the  strongly  acid  distillate  with 
an  equal  volume  of  water,  saturate  it  with 
hydrogen  sulfide  and  allow  the  beaker  to 
stand  over  night  under  a  bell  jar. 

Filter  off  the  precipitate  of  arsenic 
trisulfide  through  a  small,  well-running 
filter  and  wash  with  water  until  the 
washings  are  no  longer  acid.  Rinse  the 
precipitate  into  a  small  porcelain  dish 
and  dissolve  the  residue  on  the  filter  with 
ammonia,  washing  thoroughly  with 
water  containing  ammonia.  Concen- 
trate the  solution  to  remove  the  excess 

of  ammonia  and  evaporate  to  dryness  after  adding  concentrated 
nitric  acid.  Add  a  few  drops  of  concentrated  nitric  acid,  to 
help  oxidize  the  residual  sulfur,  and  evaporate  on  the  steam 
bath.  Dissolve  the  residue  of  arsenic  acid  in  a  little  water,  filter 
through  a  small  filter  and  concentrate  the  filtrate,  in  a  small 
beaker,  to  a  volume  of  10  to  20  c.c.  Add  2  or  3  c.c.  of  magnesia 
mixture  (cf.  p.  93),  half  the  solution's  volume  of  ammonia  water 
(d.  0.96)  and  stir  vigorously  with  a  glass  rod.  The  precipitate 
of  magnesium  ammonium  arsenate  soon  begins  to  form.  After 
a  short  time  add  a  little  more  magnesia  mixture  to  see  if  any 
further  precipitation  takes  place.  Finally  add  alcohol  corre- 
sponding to  one-fourth  the  volume  of  the  liquid  and  allow  the 
precipitate  to  stand  over  night. 

15 


FIG.     26.— 

arsenic  determination. 


226 


CHEMICAL  ANALYSIS  OF  METALS 


Filter  off  the  precipitate  through  a  weighed  Gooch  or  Munroe 
crucible  and  wash  with  2.5  per  cent  ammonia  to  the  disappear- 
ance of  chlorides.  Dry  the  crucible  and  its  contents  at  110°  and 
then  heat  it  in  air  bath  (cf.  Fig.  17,  p.  83),  raising  the  tempera- 
ture very  gradually  until  a  light  red  heat  is  obtained.  Cool  in  a 
desiccator  and  weigh  as  magnesium  pyroarsenate,  Mg2As2O7. 

Computation. — If  s  is  the  weight  of  the  sample  and  p  the  weight 
of  the  ignited  precipitate,  then 

2As  X  p  X  100       48.27? 

~T\/f — \     r\    \/ —  =  ~         ~~  Per  cent  As 

Mg2AS2O7   X    S  S 

TEST  ANALYSES 

EXPERIMENTS  WITH  AN  ARSENIC  SOLUTION  OF  KNOWN 
ARSENIC  CONTENT 

Duplicate  determination  gave  the  values  0.0338  and  0.0332  g. 
Mg2As2O7  in  10  c.c.  of  the  arsenic  solution.  Experiments  were 
carried  out  with  10  c.c.  of  the  arsenic  solution  added  to  5  g.  of 
Kahlbaum's  pure  reduced  iron  (free  from  arsenic)  and  the  weights 
of  magnesium  arsenate  obtained  were  0.0326  and  0.0328  g. 

EXPERIMENTS  WITH  COMMERCIAL  IRON  AND  STEEL 


No. 

Material  tested 

Weight 
taken  in 
grams 

Weight  of 

Mg2As2O7 

Per  cent 
arsenic 

1 

Pig  iron  

f  a 

5 

0  0034 

0  033 

2 

Siemens-Martin  steel  

U 

.  (a 

5 
5 

0.0035 
0.0024 

0.034 
0.023 

3 
4 

Siemens-Martin  steel  
Siemens-Martin  steel 

U 

...  la 

U 

!  a 

5 
5 
5 
10 

0.0026 
0  .  0066 
0.0054 
0  0128 

0.025 
0.064 
0.052 
0  062 

U 

10 

0.0106 

0.051 

Accuracy  of  the  Process. — The  arsenic  content  of  iron  and  steel 
up  to  0.3  per  cent  As  can  be  determined  with  an  accuracy  such 
that  the  results  are  probably  correct  to  within  about  0.01  per 
cent.  It  is  necessary,  however,  to  test  all  the  reagents  used  by 
running  a  blank  experiment.  This  is  especially  necessary  be- 
cause most  hydrochloric  acid  contains  traces  of  arsenic. 


CHAPTER  XVI 
COBALT 

Cobalt  is  usually  present  to  some  extent  in  all  samples  of  iron 
and  steel  that  contain  nickel.  In  some  special  cases  this  element 
is  an  intentional  constituent. 

DETERMINATION  OF  COBALT  AS  SULFATE 

Principle. — The  complex  thiocyanates  of  nickel  and  cobalt 
may  be  separated  from  one  another  by  treatment  with  a  mixture 
of  amyl  alcohol  and  ether.1 

APPARATUS  AND  SOLUTIONS  REQUIRED 

1.  Rothe  shaking  funnel  (Fig.  13,  p.  71). 

2.  Amyl  alcohol-ether  mixture.     Mix  25  parts  by  volume  of 
ether  with  1  part  of  amyl  alcohol. 

Procedure. — If  the  nickel  content  is  fairly  high,  weigh  out 
about  5  g.  of  the  original  metal,  or  10  g.  if  the  nickel  content  is 
low.  Deposit  the  nickel  and  cobalt  electrolytically,  as  described 
on  p.  178,  and  weigh  the  deposit. 

Dissolve  the  deposited  nickel  and  cobalt  in  a  little  concentrated 
nitric  acid  (d.  1.42)  and  carefully  rinse  off  the  electrode.  To 
remove  the  excess  of  acid,  evaporate  the  solution  of  nickel  and 
cobalt  nitrates  just  to  dryness  in  a  porcelain  dish  and  dissolve 
the  residue  in  a  little  water.  For  each  0.1  g.  of  metal  present, 
add  4  g.  of  pure  ammonium  thiocyanate,2  NH4CNS,  to  the 
concentrated  solution  of  cobalt  and  nickel  nitrates.  Dissolve 
the  salt  by  means  of  a  little  water.  It  is  essential  to  have  a 
saturated  solution  at  this  point;  if  necessary,  concentrate  it  by 

1  ROSENHAIN  and  HULDSCHINSKY  (Ber.,  34,  2,050  (1901))  first  proposed 
the  quantitative  application  of  Vogel's  sensitive  test  for  cobalt  in  the  pres- 
ence of  nickel  (Ber.,  12,  2,314  (1879)). 

2  Commercial  ammonium  thiocyanate  is  often  impure.     It  is  absolutely 
necessary  that  no  weighable  residue  should  be  obtained  on  heating  the 
salt. 

227 


228  CHEMICAL  ANALYSIS  OF  METALS 

evaporation  on  the  water  bath.  Transfer  the  concentrated 
solution  to  the  upper  bulb  of  the  Rothe  shaking  funnel  and  rinse 
out  the  evaporating  dish  with  a  little  saturated  ammonium 
thiocyanate  solution.  Then  add  60  to  80  c.c.  of  the  amyl  alcohol- 
ether  mixture  and  shake  vigorously.  After  the  mixture  has 
become  perfectly  quiet,  the  upper  layer  in  the  funnel  is  a  beautiful 
blue  even  when  only  a  little  cobalt  is  present.1  The  cobalt  is 
present  in  the  ether  layer  as  complex  ammonium  cobalti-thio- 
cyanate  and  the  nickel  remains  in  the  aqueous  solution  as  simple 
thiocyanate.  Allow  the  lower  layer  in  the  upper  bulb  of  the 
funnel  to  run  into  the  lower  bulb  and  rinse  the  former  with  a 
little  saturated  ammonium  thiocyanate  solution.  Add  10  c.c. 
more  of  saturated  ammonium  thiocyanate  solution  to  the  con- 
tents of  the  upper  bulb  and  40  c.c.  of  the  ether  mixture  to  the 
lower  bulb  and  again  shake  vigorously.  In  this  way  the  remain- 
der of  the  nickel  in  the  upper  bulb  is  washed  away  from  the 
ether  and  a  little  cobalt  in  the  lower  bulb  is  dissolved  by  the 
ether.  Allow  the  liquids  to  stand  until  two  layers  are  well 
separated  in  each  bulb,  and  then  transfer  the  green  nickel  solu- 
tion in  the  lower  bulb  to  a  beaker  and  wash  out  the  stopcock 
boring,  etc.,  with  a  little  ammonium  thiocyanate  solution.  Then 
transfer  the  aqueous  layer  in  the  upper  bulb  to  the  lower  bulb, 
and  rinse  the  upper  bulb  with  a  little  ammonium  thiocyanate 
solution.  Add  5  or  10  c.c.  of  dilute  sulfuric  acid  (1 : 10)  to  the 
upper  bulb,  close  the  stopcock  and  shake  well.  The  blue  color 
of  the  amyl  alcohol-ether  mixture  will  now  disappear  and  the 
cobalt  will  pass  into  the  dilute  sulfuric  acid  solution,  imparting 
a  pink  color  to  it.  The  aqueous  thiocyanate  solution  in  the 
lower  bulb  contains  traces  of  nickel.  Allow  it  to  flow  into 
the  beaker  and  rinse  the  bulb  in  the  usual  manner.  Then 
transfer  the  cobalt  sulfate  solution  in  the  upper  bulb  into  the 
lower  bulb  and  rinse  the  ether-alcohol  remaining  in  the  upper 
bulb  with  a  few  drops  of  dilute  sulfuric  acid.  By  shaking, 
the  blue  ether  solution  in  the  lower  bulb  is  now  decolorized.2 
Transfer  the  sulfuric  acid  solution  of  cobalt  sulfate  to  a  weighed 
porcelain  crucible,  rinse  the  ether-alcohol  mixture  in  each  bulb 

1  If  a  little  iron  is  present  the  red  color  of  ferric  thiocyanate  causes  a 
composite  colored  layer  and  the  iron  contaminates  the  final  cobalt  sulfate. 

2  Usually  the  ether  is  colored  reddish-brown  by  a  little  ferric  thiocyanate. 


COBALT  229 

with  small  portions  of  dilute  sulfuric  acid  and  add  the  washings 
to  the  contents  of  the  crucible.  Evaporate  to  dryness  and  heat 
to  destroy  organic  matter  and  finally  to  remove  the  excess  of 
sulfuric  acid,  as  described  under  Manganese,  p.  82.  Weigh  the 
pink  cobalt  sulfate  and  then  test  it  for  impurities.  Dissolve  it 
in  a  little  water  and  add  ammonia  until  the  solution  is  weakly 
ammoniacal.  If  a  precipitate  of  ferric  hydroxide  is  formed,  filter 
it  off  and  weigh  it.  Add  dimethylglyoxime  solution,  drop  by 
drop,  as  long  as  any  precipitate  continues  to  form.  Allow  the 
solution  to  stand  J^  hr.  in  a  warm  place  and  then  filter  off  the 
precipitate  of  nickel  salt  upon  a  small  filter.  Wash  it  thoroughly 
with  hot  water,  ignite  it  and  weigh  as  nickelous  oxide,  NiO. 

The  quantity  of  cobalt  present  is  computed  by  deducting  from 
the-  original  weight  of  cobalt  sulfate,  the  weight  of  ferric  oxide1 
obtained,  and  of  nickel  sulfate  corresponding  to  the  weight  of 
oxide  obtained  after  igniting  the  glyoxime  precipitate. 

To  weigh  the  cobalt  itself  after  purification,  evaporate  the 
filtrate  from  the  nickel  precipitate  in  a  weighed  porcelain  crucible, 
ignite  the  residue  after  moistening  it  with  a  little  nitric  acid  and 
a  drop  of  sulfuric  acid,  and  heat  to  constant  weight  as  described 
under  Manganese,  p.  82.  Or,  the  cobalt  sulfate  solution  may 
be  dissolved  in  water  and  the  ammoniacal  solution  electrolyzed 
as  described  under  Nickel,  p.  178. 

Computation. — If  p  represents  the  weight  of  pure  cobalt  sulfate 
obtained  in  the  analysis  of  s  g.  of  metal,  then 

38.03  p 
per  cent  Co  =  - 

Test  Analyses. — (1)  Separation  of  Nickel  and  Cobalt  in  Solutions 
of  Pure  Salts. — Twenty-five-cubic-centimeter  portions  of  a  nickel 
chloride  solution  containing  0.0245  g.  nickel  were  mixed  with 
25-c.c.  portions  of  cobalt  chloride  solution  containing  0.0110  g. 
cobalt.  The  cobalt  was  determined  as  sulfate  according  to  the 
above  directions  and  in  three  experiments  the  results  obtained 
were  0.0115  and  0.0114  and  0.0122  g.  cobalt.  The  cobalt  sulfate 
obtained  in  the  third  experiment  was  impure.  It  was  dissolved 
and  the  ammoniacal  solution  electrolyzed;  0.0114  g.  cobalt  was 
then  obtained. 

1  Ferric  sulfate  changes  to  ferric  oxide  and  sulfuric  anhydride  at  tempera- 
tures at  which  nickel,  cobalt  and  manganese  sulfates  are  more  stable. 


230  CHEMICAL  ANALYSIS  OF  METALS 

2.  Analysis  of  Nickel  Steel. — The  nickel  and  cobalt  were  deter- 
mined together  by  the  electrolytic  method  described  on  p.  178. 
The  results  of  two  experiments  gave  the  values  23.50  and  23.46 
per  cent  Ni  -f  Co.     From  the  electrolytic  deposit,  the  impure 
cobalt  sulfate  obtained  by  the  above  method  indicated  0.66  and 
0.67  per  cent  Co  but  after  dissolving  the  sulfate  and  determining 
the  cobalt  electrolytically  the  results  were  0.38  and  0.39  per  cent 
Co. '  The  values  obtained  by  deducting  the  weight  of  the  nickel 
as  determined  by  precipitation  with  dimethylglyoxime  from  the 
weight  of  the  cobalt  and  nickel  deposit,  averaged  0.51  per  cent. 

3.  Cobalt  Content  of  Commercial  Nickel. — Duplicate  determi- 
nations of  the  cobalt  content  of  a  sample  of  commercial  nickel 
gave  the  values  0.88  and  0.89  per  cent  cobalt.1 

1  Commercial  nickel  sometimes  contains  a  little  zinc.  This  will  come 
down  with  the  cobalt  in  the  electrolytic  determination  and  will  also  follow 
the  cobalt  in  the  potassium  thiocyanate  separation. 


CHAPTER  XVII 
TITANIUM 

Pig  iron  prepared  from  ores  containing  titanium  often  contains 
small  quantities  of  this  element.  Moreover,  titanium,  like 
aluminium,  is  used  as  a  deoxidizing  agent  and  in  some  cases  a 
little  of  the  titanium  gets  into  the  metal  in  this  way.  Usually, 
however,  the  quantity  of  titanium  used  is  regulated  so  that  all 
of  it  goes  into  the  slag. 

Ferro-titanium  and  manganese-titanium  are  the  principle  al- 
loys of  titanium  that  are  used  in  metallurgical  operations. 

1.  DETERMINATION  OF  TITANIUM  IN  MATERIALS  SOLUBLE 

IN  ACID 

Principle. — Titanium  may  be  freed  from  the  greater  part  of 
the  iron  by  means  of  the  Rothe  ether  separation  (p.  71).  After 
the  ether  treatment,  the  solution  contains  manganese,  nickel, 
chromium,  possibly  some  other  metals  and  phosphoric  acid 
besides  the  titanium  and  a  little  of  the  iron. 

The  titanium  may  be  precipitated  from  such  a  solution  by 
boiling  an  acetic  acid  solution1  containing  ammonium  acetate 
and  something  to  keep  iron  in  the  ferrous  condition,  but  in  most 
cases  it  is  necessary  to  purify  the  titanium  dioxide  that  is  obtained 
by  such  a  procedure.  The  weight  of  the  impurities  is  deducted 
from  the  weight  of  impure  titanium  dioxide.  The  titanium  may 
also  be  determined  colorimetrically,  or,  if  the  titanium  content  is 
not  too  low,  it  may  be  determined  by  a  volumetric  process.2 

Apparatus  and  Solutions  Required. — 

FOR  THE  ETHER  TREATMENT: 

Rothe  shaking  funnel,  Fig.  13,  p.  71. 

Hydrochloric  acid  (d.  1.10). 

Ether-hydrochloric  Acid  Solutions. — One  solution  is  made  by  adding 
ether  to  concentrated  hydrochloric  acid  (d.  1.2)  until  a  layer  of 
ether  is  formed  after  shaking,  and  the  other  solution  is  prepared 
from  dilute  hydrochloric  acid  (d.  1.10),  in  the  same  way. 

1  cf.  BARNEBEY  and  ISHAM,  /.  Am.  Chem.  Soc.,  32,  957  (1910). 

2  cf.  HINRICHSEN,  Chem.  Ztg.}  31,  738  (1907). 

231 


232  CHEMICAL  ANALYSIS.  OF  METALS 

FOR  TITRATING  THE  TITANIUM: 

Ferric  Chloride  Solution. — Moisten  27  g.  of  pure  ferric  chloride  crystals 
(FeCl3.  6H2O)  with  10  c.c.  of  hydrochloric  acid  (d.  1.12), 
dissolve  by  warming  with  water  and  dilute  the  solution  to  1  liter. 
The  hydrochloric  acid  is  necessary  to  prevent  hydrolysis  of  the 
ferric  chloride,  whereby  a  basic  chloride  is  precipitated  which 
makes  the  solution  unfit  for  use. 

The  ferric  chloride  solution  may  be  standardized  against 
tenth-normal  sodium  thiosulfate  solution  (cf.  p.  171)  or  against 
tenth-normal  permanganate  (p.  172). 

To  standardize  against  sodium  thiosulfate  solution,  measure 
out  by  means  of  a  burette  or  pipette  35  to  50  c.c.  of  the  ferric  chlo- 
ride solution  into  a  200-c.c.  Erlenmeyer  flask  and  concentrate  to 
about  15  c.c.  Add  2  c.c.  of  dilute  hydrochloric  acid  (d.  1.12), 
and  a  solution  of  3  g.  potassium  iodide  dissolved  in  a  little  water; 
the  potassium  iodide  must  be  free  from  iodate  and  its  aqueous 
solution  should  remain  colorless  upon  the  addition  of  a  little 
hydrochloric  acid.1  By  means  of  hydriodic  acid,  ferric  ions  are 
reduced  to  ferrous  ions  and  iodine  is  set  free: 

2Fe+++  +  21-  =  2Fe++  -f  I2 

The  iodine  is  titrated  with  tenth-normal  sodium  thiosulfate  solu- 
tion, adding  starch  solution  toward  the  last.  To  reduce  traces  of 
ferric  chloride  that  still  remain  in  the  solution,  heat  to  50°,  or 
60°  at  the  most,  cool  to  room  temperature  by  running  cold  water 
upon  the  flask,  add  a  little  more  starch  solution  and  finish  the 
titration  with  sodium  thiosulfate. 

To  standardize  against  potassium  permanganate,  the  Zimmer- 
mann-Reinhardt  method2  is  suitable.  Measure  out,  by  means  of 
pipette  or  burette,  25  to  50  c.c.  of  the  ferric  chloride  solution  into  a 
small  beaker,  add  10  c.c.  of  hydrochloric  acid  (d.  1.12),  and 
heat  the  solution  nearly  to  boiling.  Place  the  beaker  on  a  piece 
of  white  filter  paper  and  add  stannous  chloride  solution  (50  g. 
stannous  chloride  crystals,  and  100  c.c.  concentrated  hydrochloric 
acid;  heat  till  dissolved  and  dilute  with  water  to  1  liter),  drop  by 
drop,  until  the  yellow  color  of  ferric  chloride  disappears  from  the 
hot  solution.  Take  pains  not  to  add  a  single  drop  of  the  stannous 

1  If  iodine  is  liberated,  an  allowance  for  this  must  be  made  in  the  analysis. 

2  ZIMMERMANN,  Ber.,  14,  779    (1881);    REINHARDT,   Chem-Ztg.,   13,  323 
(1884). 


TITANIUM  233 

chloride  in  excess  of  the  quantity  necessary  to  render  the  solu- 
tion colorless.  If  more  is  used  by  accident,  add  a  few  drops  of 
potassium  permanganate  solution  to  oxidize  the  excess  stannous 
chloride  and  enough  of  the  iron  to  give  a  slight  yellow  color 
(ferric  chloride)  to  the  solution  and  repeat  the  reduction  with 
stannous  chloride.  Cool  the  solution  to  room  temperature  and 
quickly  add  10  c.c.  of  mercuric  chloride  solution  (50  g.  in  one  liter 
of  water).  Allow  the  solution  to  stand  5  min.  to  complete  the 
reaction  between  the  excess  stannous  chloride  and  the  mercuric 
chloride,  whereby  a  silky  precipitate  of  mercurous  chloride  is 
formed,  then  dilute  to  about  400  c.c.  and  add  20  c.c.  of  acid  man- 
ganese sulfate  solution  (prepared  by  dissolving  67  g.  of  mangan- 
ous  sulfate  crystals,  MnSO4-4H2O,  in  500  c.c.  water,  adding  138. 
c.c.  of  phosphoric  acid  (d.  1.7),  and  130  c.c.  of  sulfuric  acid 
(d.  1.84),  and  diluting  to  1  liter).  After  the  addition  of  the 
manganese  sulfate  solution,  titrate  the  ferrous  solution  slowly 
with  tenth-normal  permanganate.  At  no  time  should  the  solu- 
tion of  permanganate  be  added  faster  than  the  drops  can  be 
counted  and  it  is  important  at  the  start  and  finish  not  to  add  a 
drop  of  permanganate  until  the  color  produced  by  the  previous 
drop  has  disappeared  entirely. 

This  method  of  standardization  gives  good  results  with  a  little 
practice.  It  is  necessary  to  add  the  manganese  sulfate  solution 
as  otherwise  the  dilute  hydrochloric  acid  is  oxidized  by  the  per- 
manganate in  the  presence  of  ferrous  salt,  and  the  results  of  the 
standardization  will  be  too  low  on  account  of  the  use  of  too  much 
permanganate.  It  is  important  to  follow  the  directions  very 
carefully. 

Procedure. — Weigh  out  10  to  15  g.  of  the  iron  or  steel  into  a 
porcelain  dish,  and  dissolve  it  in  nitric  acid  (d.  1.18),  using 
about  12  c.c.  of  acid  for  each  gram  of  sample.  Evaporate  the 
solution  to  dryness,  take  up  in  hydrochloric  acid  and  remove  the 
silica  in  the  usual  way  (p.  121).  The  silica  carries  down  a  little 
titanium  dioxide  with  it.  After  volatilizing  the  silicon  as  tetra- 
fluoride,  therefore,  fuse  the  residue  with  sodium  carbonate,  dis- 
solve the  melt  in  hydrochloric  acid  (d.  1.12)  and  add  the  solution 
to  the  nitrate  from  the  silica. 

Concentrate  the  solution  and  remove  the  ferric  chloride  as 
completely  as  possible  by  the  ether  method  (p.  71).  The  pres- 


234  CHEMICAL  ANALYSIS  OF  METALS 

ence  of  titanium  is  often  betrayed  by  the  hydrochloric  acid  solu- 
tion becoming  somewhat  turbid  after  the  first  shaking  with  ether 
and  more  turbid  after  the  second  shaking,  when  flakes  of 
titanium  dioxide  are  deposited  sometimes.  Such  precipitates  are 
often  colored  pale  yellow  by  a  little  peroxide  in  the  ether.  If 
the  titanium  content  is  low,  a  clear  solution  is  obtained  which  is 
usually  brownish-yellow  on  account  of  the  formation  of  a  little 
pertitanic  acid  by  peroxide  in  the  ether.  The  precipitation  of 
titanium  dioxide  during  the  ether  treatment  is  due  to  hydrolysis 
and  is  caused  by  the  fact  that  ether  removes  some  of  the  hydro- 
chloric acid  which  was  necessary  to  prevent  hydrolysis;1 

Ti++++  +  4H2O^Ti(OH)4  +  4H+ 

Under  the  proper  conditions,  the  quantity  of  iron  remaining 
with  the  titanium  after  the  ether  separation  in  the  aqueous  solu- 
tion is  very  small.  Evaporate  off  the  dissolved  ether  by  heating 
on  the  water  bath  and  continue  the  evaporation  to  dryness.  Add 
a  little  concentrated  hydrochloric  acid  to  the  residue,  whereby 
some  of  the  titanium  remains  undissolved  as  TiO2,  dilute  to 
150  c.c.  without  filtering  and  add  3  g.  of  solid  ammonium  acetate. 
Heat  the  solution  to  boiling  and  keep  gently  boiling  for  a 
few  minutes.  All  the  titanium  is  then  precipitated  as  dioxide 
contaminated  with  ferric  basic  acetate.  Allow  the  precipitate 
to  settle  and  then  filter.  Test  the  filtrate  with  hydrogen  per- 
oxide to  see  if  any  titanium  remains.  If  so,  boil  the  solution 
15  min.  longer.  Wash  the  precipitate  with  water  containing 
ammonium  acetate,  ignite  and  weigh.  The  precipitate  is  almost 
always  contaminated  with  some  iron.  The  true  titanium  content 
may  be  determined  by  one  of  the  three  following  methods. 

(a)  Colorimetric  Determination. — Fuse  the  ignited  titanium 
oxide  precipitate  with  15  to  20  times  as  much  of  previously-  dehy- 
drated potassium  pyrosulfate,  K2S2O7,  which  is  prepared  by 
heating  potassium  acid  sulfate  in  a  platinum  crucible  until  fumes 
of  sulfuric  anhydride  are  evolved.  After  fusing,  cool  the  crucible 
and  dissolve  the  melt  in  75  c.c.  of  cold  water  and  5  c.c.  of  concen- 
trated sulfuric  acid.  If  an  insoluble  residue  remains  it  must 

1  If  the  concentration  of  the  hydrochloric  acid  was  6-normal  (i.e., 
d.  1.1),  there  is  little  danger  of  any  TiO2  being  precipitated.  Care  must 
be  taken  not  to  dilute  the  solution  much  below  this  concentration. 


TITANIUM  .235 

be  fused  again  with  potassium  pyrosulfate.  Dilute  the  solution 
to  100  c.c.  in  a  calibrated  flask  and  use  50  c.c.  or  less,  according 
to  the  titanium  content,  for  the  colorimetric  comparison. 

To  prepare  a  standard  solution  of  titanium,  weigh  0.4996  g.  of 
pure  anhydrous  potassium  titanium  fluoride,  K2TiF6,  into  a 
platinum  crucible.  To  remove  fluorine  and  form  potassium 
sulfate  and  titanium  sulfate,  heat  the  salt  with  a  little  water  and 
concentrated  sulfuric  acid  until  fumes  are  evolved,  and  repeat 
the  treatment  several  times.  Finally  dissolve  the  titanium 
sulfate  by  heating  with  a  little  concentrated  sulfuric  acid  and 
dilute  with  5  per  cent  sulfuric  acid  to  100  c.c.  One  cubic  centi- 
meter of  this  solution  contains  0.001  g.  of  titanium.  Or,  the 
standard  solution  may  be  prepared  by  fusing  0.1665  g.  of  pure 
titanium  dioxide  with  eight  times  as  much  sodium  carbonate, 
dissolving  the  excess  sodium  carbonate  in  cold  water,  filtering 
and  dissolving  the  residue  of  sodium  acid  titanate  in  10  c.c.  of  con- 
centrated sulfuric  acid  and  finally  diluting  the  solution  to  exactly 
100  c.c.  at  room  temperature.  One  cubic  centimeter  of  standard 
solution  contains  0.001  g.  titanium.1 

Prepare  a  series  of  standards  by  measuring  out  1,  3,  5,  10-c.c., 
etc.,  portions  of  the  standard  titanium  solution,  diluting  each  to 
50  c.c.  in  a  Nessler  tube  with  5  per  cent  sulfuric  acid,  adding  2  c.c. 
of  hydrogen  peroxide  (free  from  fluorine)  and  mixing.  Compare 
with  the  standards  the  color  produced  with  an  aliquot  part  of  the 
solution  to  be  analyzed  and  2  c.c.  of  hydrogen  peroxide.  The 
color  in  the  case  of  dilute  solutions  may  be  compared  by  looking 
down  upon  the  tubes  against  a  white  background.  Another 
method  is  to  place  the  tube  side  by  side  in  a  colorimeter  with  a 
weaker  standard  and  dilute  the  unknown  solution  with  measured 
volumes  of  5  per  cent  sulfuric  acid,  mixing  after  each  addition, 
until  the  two  solutions  are  of  the  same  color  and  dilution.  In 
this  case  the  tubes  are  held  side  by  side  and  viewed  horizontally. 
From  the  known  amount  of  titanium  present  in  the  standard  it  is 
easy  to  compute  that  present  in  the  unknown  solution. 

1  The  standard  solution  can  be  prepared  even  more  easily  by  digesting 
0.1665  g.  of  pure  titanium  oxide  with  10  c.c.  of  hot,  concentrated  sulfuric  acid 
in  a  porcelain  dish.  When  the  oxide  has  all  dissolved,  cool  and  very  care- 
fully dilute  to  exactly  100  c.c.  at  room  temperature.  Usually  the  acid 
gently  ignited  to  titanium  oxide  obtained  in  the  analysis  can  be  dissolved 
by  digesting  with  hot  concentrated  sulfuric  acid. 


236  CHEMICAL  ANALYSIS  OF  METALS 

This  colorimetric  method  is  the  most  satisfactory  for  the 
determination  of  small  quantities  of  titanium.  In  most  cases  a 
satisfactory  analysis  can  be  made  with  a  sample  of  iron  or  steel 
weighing  only  1  g.  The  method  is  not  suitable  for  large  amounts 
of  titanium,  as  the  color  of  the  pertitanic  acid  is  best  estimated  in 
dilute  solutions  and  when  more  than  1  per  cent  of  titanium  is 
present  a  very  small  aliquot  part  of  the  sample  has  to  be  taken. 
The  solution  should  contain  at  least  5  per  cent  of  sulfuric  acid 
when  the  test  is  made  and  molybdenum,  vanadium  or  chromium 
must  not  be  present  as  each  of  these  elements  gives  a  color  reac- 
tion with  hydrogen  peroxide.  The  test  is  so  delicate  that  one 
part  of  titanium  can  be  detected  in  the  presence  of  one  million 
parts  of  water. 

Computation.  —  If  nz  c.c.  of  the  standard  solution  match  the 
color  produced  with  n\  c.c.  of  the  100-c.c.  solution  obtained  from 
s  g.  of  metal,  then 


,  ™. 
=  per  cent  Ti 


Or,  if  it  was  necessary  to  dilute  n\  c.c.  of  the  analyzed  solution 
with  t  c.c.  of  5  per  cent  sulfuric  acid  before  getting  a  shade  corre- 
sponding to  HZ  c.c.  of  standard  in  50  c.c.  of  solution,  then 

0.2(ni  +  0w2 

-  =  per  cent  Ti 
ni  X  s 

(b)  Volumetric  Determination.  —  Fuse  the  impure  titanium 
oxide  in  a  platinum  crucible  with  about  ten  times  its  weight  of 
sodium  carbonate.  Cool,  place  the  crucible  in  a  beaker  and  cover 
it  with  cold  water.  After  all  the  sodium  carbonate  has  dissolved, 
filter  off  the  solution  from  the  insoluble  sodium  acid  titanate  and 
ferric  oxide  and  wash  the  residue  with  cold  water.  Allow  the 
funnel  to  drain  completely,  pierce  the  filter  with  a  pointed  glass 
rod,  and  wash  the  precipitate  into  a  small  Erlenmeyer  flask  with 
dilute  hydrochloric  acid  (d.  1.12).  Wash  the  filter  with  hot 
hydrochloric  acid  of  the  same  strength  and  heat  this  acid  with 
the  residue  until  all  the  sodium  titanate  and  ferric  oxide  have 
dissolved.  Acid  more  dilute  than  this  will  not  dissolve  the 
precipitate.  If  this  point  is  forgotten  and  water  is  added,  hy- 
drolysis takes  place  and  the  titanium  is  precipitated.  Such  a 
precipitate  is  very  hard  to  filter  and  wash,  so  that  it  is  very  easy 
to  spoil  the  analysis  at  this  point. 


TITANIUM 


237 


Concentrate  the  solution  to  about  20  c.c.  in  a  200-c.c.  Erlen- 
meyer  flask.  Add  10  to  20  c.c.  of  concentrated  hydrochloric 
acid  (d.  1.2)  and  close  the  flask  with  a  rubber  stopper  carrying 
a  Bunsen  valve  on  the  outside.  To  make  a  Bunsen  valve,  insert 
a  piece  of  glass  tubing  into  a  one-hole  rubber  stopper  and  on 
the  glass  tubing  place  a  short  piece  of  rubber  tubing  sealed  at 
the  other  end  with  a  piece  of  stirring  rod.  Make  a  slit  in  the 
side  of  the  tubing  to  permit  gas  to  escape  from  the  flask;  pressure 
from  the  outside  squeezes  the  cut  ends  of  the  rubber  together 
so  that  air  from  the  outside 
cannot  enter  the  flask.  Bet- 
ter still,  the  flask  may  be 
connected,  as  shown  in  Fig. 
27,  with  a  beaker  contain- 
ing a  saturated  solution  of 
sodium  bicarbonate.1  Then 

if  there  is  any  back  pressure,     FIG.  27.  —  Apparatus  for  reducing  titanium 

sodium  bicarbonate  is  sucked  solutions. 

into  the  flask  which  causes  evolution  of  carbon  dioxide  and  thus 

prevents  air  from  entering. 

To  reduce  the  titanium  from  the  quadrivalent  to  trivalent 
condition,  introduce  a  piece  of  50  per  cent  zinc-magnesium  alloy, 
weighing  about  2  g.  or  about  3  g.  of  stick  zinc  in  coarse  pieces.  It 
is  not  necessary  that  the  zinc  should  be  abs.olutely  free  from  iron. 
Stopper  the  flask  and  allow  the  reduction  to  take  place  for  a  time 
in  the  cold.  When  the  solution  has  become  violet  and  most  of  the 
zinc  has  dissolved,  add  1  or  2  g.  more  of  the  metal,  in  coarse  pieces, 
close  the  flask  quickly,  and  finish  the  reduction  by  heating  on  the 
water  bath. 

During  the  reduction,  the  following  reaction  takes  place: 


Zn(or  Mg)  = 


Zn++(or  Mg++) 


To  accomplish  the  reduction,  it  is  necessary  to  get  all  of  the 
quadrivalent  titanium  into  the  ionic  condition.  In  attempting 
to  reduce  a  slightly  acid  titanium  solution,  the  reduction  is 
usually  incomplete  on  account  of  hydrolysis  even  when  there  is  no 
visible  precipitation  of  titanium  dioxide,  for  the  hydrated  oxide 

1  A  Contat-Gockels  valve  works  very  nicely.  See  Z.  angew.  Chem.,  13, 
620  (1899),  or  TREADWELL-HALL,  "Analytical  Chemistry"  vol.  II. 


238  CHEMICAL  ANALYSIS  OF  METALS 

may  remain  in  colloidal  solution.  In  such  cases  the  titration  will 
give  too  low  results.  For  this  reason,  it  is  necessary  to  have  the 
titanium  solution  strongly  acid  to  get  a  complete  reduction. 

Instead  of  using  a  small  quantity  of  zinc  and  waiting  till  all  has 
dissolved,  a  larger  piece  of  metal  may  be  used  and  suspended  in 
the  solution,  as  shown  in  the  drawing,  by  means  of  fine  platinum 
wire.  After  reducing  for  three-quarters  of  an  hour  to  an  hour, 
allow  the  solution  to  cool  and  then  remove  the  excess  of  zinc, 
rinsing  it  with  cold  water. 

Add  to  the  solution  1  or  2  g.  of  pure  ammonium  thiocyanate, 
free  from  iron,  and  titrate  with  ferric  chloride  solution  until  a 
permanent  red  color,  due  to  ferric  thiocyanate,  is  obtained. 

Computation. — If  n  c.c.  of  ferric  chloride  solution,  of  which  1 
c.c.  =  t  g.  of  titanium,  are  used  in  the  analysis  of  a  sample  weigh- 
ing s  g.,  then 

per  cent  Ti  =  1002- 
or,  in  case  the  ferric  chloride  solution  was  exactly  tenth-normal, 

per  cent  Ti  =  -  0.481 

s 

(c)  Determination  of  Iron  in  Impure  Titanium  Oxide. — Inas- 
much as  the  impurity  present  in  the  ignited  precipitate  of  tita- 
nium oxide  is  chiefly  ferric  oxide,  the  quantity  of  titanium  dioxide 
may  be  estimated  with  fair  accuracy  by  determining  the  amount 
of  iron  by  titration  and  then  deducting  the  corresponding  amount 
of  ferric  oxide  from  the  weight  of  impure  titanium  oxide. 

The  volumetric  determination  of  the  iron  may  be  accomplished 
in  the  hydrochloric  acid  solution  obtained  after  fusing  the  impure 
titanium  oxide  with  sodium  carbonate  (p.  236)  by  the  iodometric 
method  described  on  p.  170,  or  by  the  following  method,  in 
which  tenth-normal  permanganate  is  used. 

Titanium  is  reduced  from  the  quadrivalent  to  trivalent  condi- 
tion less  readily  than  iron  is  reduced  from  the  ferric  to  ferrous 
state.  Thus  metallic  zinc,  which  is  so  often  used  for  reducing 
ferric  solutions  previous  to  titration  with  permanganate,  begins 
to  reduce  titanium  after  the  ferric  ions  are  all  reduced  and  the 
reduction  is  more  or  less  complete  according  to  the  conditions. 
If  the  conditions  are  as  described  in  the  previous  method,  a 


TITANIUM  239 

quantitative  reduction  of  both  iron  and  titanium  takes  place. 
Stannous  chloride,  recommended  on  p.  232,  also  reduces  titanium 
solutions,  although  it  is  possible,  with  a  little  practice,  to  reduce 
the  iron  and  practically  no  titanium,  by  stopping  the  addition 
of  the  reagent  at  the  exact  point  where  the  solution  becomes 
colorless;  further  addition  of  stannous  chloride  causes  the  forma- 
tion of  violet,  trivalent  titanium  ions. 

Probably  the  most  satisfactory  reducing  agent,  however,  for 
reacting  with  ferric  ions  in  the  presence  of  titanium  is  hydrogen 
sulfide  in  sulfuric  acid  solution. 

Procedure. — Fuse  the  impure  titanium  dioxide  with  potassium 
pyrosulfate  and  dissolve  the  melt  as  directed  on  p.  234.  Transfer 
the  solution  to  a  200-c.c.  flask  which  is  fitted  with  a  rubber  stopper 
carrying  two  glass  tubes  by  which  gas  can  enter  and  leave  the 
flask.  The  tubes  are  each  bent  once  at  right  angles  and  the  one 
through  which  the  hydrogen  sulfide  is  to  enter  reaches  nearly  to 
the  bottom  of  the  flask,  while  the  other  extends  just  to  the  lower 
edge  of  the  rubber  stopper.  The  solution  to  be  reduced  should 
contain  about  one-tenth  its  volume  of  concentrated  sulfuric  acid. 
Heat  the  solution  to  boiling  while  passing  hydrogen  sulfide  gas 
through  it.  With  the  small  amount  of  iron  present,  a  few  min- 
utes should  suffice  for  the  complete  reduction  of  the  ferric  ions. 
Continue  boiling  the  solution  gently  and  replace  the  stream  of 
hydrogen  sulfide  with  one  of  carbon  dioxide  and  pass  this  gas 
through  the  solution  until  it  ceases  to  blacken  lead  acetate  paper 
as  it  leaves  the  flask.  Cool  in  a  slow  stream  of  carbon  dioxide 
and  titrate  with  potassium  permanganate. 

Computation. — If  p  g.  of  impure  TiO2  were  obtained  in  the 
analysis  of  s  g.  of  the  original  material  and  the  only  impurity  was 
ferric  oxide  which  required  n  c.c.  of  permanganate  which  was/- 
normal,  then 

per  cent  Ti  =  60.05  (P-0-7985"^' 

s 

2.     DETERMINATION  OF  TITANIUM  IN  INSOLUBLE  MATERIALS 

(Ferro-titanium  and  other  Titanium  Alloys) 

Procedure. — Heat  1  to  2  g.  of  the  material  which  should  be 
pulverized  as  finely  as  possible,  in  a  platinum  crucible  with  five 


240  CHEMICAL  ANALYSIS  OF  METALS 

or  six  times  as  much  of  a  mixture  of  1  part  magnesium  oxide  and 
2  parts  of  anhydrous  sodium  carbonate  (cf.  p.  125).  Mix  the 
sample  with  the  ignition  mixture  and  introduce  it  into  the  crucible 
after  first  covering  the  bottom  with  a  layer  of  the  ignition  mixture. 
Carry  out  the  fusion  as  directed  on  p.  125. 

Transfer  the  ignited  mass  to  an  agate  mortar,  moisten  it  with 
a  little  cold  water  and  triturate  to  a  paste.  Rinse  the  paste  into  a 
beaker  using  as  little  water  as  possible.  Add  to  the  contents  of 
the  beaker  five  or  six  times  as  much  concentrated  hydrochloric 
acid  (d.  1.2)  as  there  is  water  in  the  beaker,  cover  with  a  watch- 
glass  to  prevent  loss  by  spattering,  and  heat  gently,  stirring 
from  time  to  time.  If  the  directions  are  carefully  followed,  a 
clear  solution  will  be  obtained  in  a  short  time. 

Concentrate  the  hydrochloric  acid  solution,  transfer  it  to  a 
200  c.c.  Erlenmeyer  flask,  reduce  with  zinc  and  titrate  as  de- 
scribed on  p.  237. 

If  the  titanium  content  is  high  it  may  be  advisable  to  use  an 
aliquot  part  of  the  solution.  In  this  case  do  not  concentrate  the 
hydrochloric  acid  solution  of  the  melt,  but  dilute  it  with  hydro- 
chloric acid  (d.  1.12)  to  250  c.c.  in  a  calibrated  flask  and  use 
100  c.c.  for  the  titration,  first  concentrating  the  solution. 

In  some  cases  muddy,  violet-colored  solutions  are  obtained 
after  the  reduction  with  zinc.  This  is  due  to  some  impurity  such 
as  molybdenum  or  tungsten.  In  such  cases  it  is  advisable  to  pro- 
ceed somewhat  differently  in  order  to  remove  the  impurities. 
Extract  the  product  of  the  first  ignition  with  hot  water  and  wash 
the  insoluble  residue  of  magnesium  oxide  and  sodium  acid  titanate 
very  thoroughly  with  hot  water.  Ignite  the  filter  and  its  contents 
in  a  platinum  crucible  till  the  filter  is  all  consumed,  mix  the  resi- 
due with  three  or  four  times  as  much  sodium  carbonate  as  the  origi- 
nal sample  weighed,  and  again  heat  strongly.  Remove  the  melt 
from  the  crucible  with  the  aid  of  a  little  cold  water,  and  dissolve  in 
hydrochloric  acid  as  described  above. 

Test  Analyses.  (1)  Experiments  with  Titanium  Solutions. 
A  titanium  solution  was  prepared  and  titanium  dioxide  deter- 
mined by  precipitation  from  acetic  acid  solution.  Duplicate 
experiments  gave  0.0961  and  0.0978  g.  TiO2  corresponding 
respectively  to  0.0577  and  0.0587  g.  Ti. 

Twenty  cubic  centimeters  of  titanium  solution  were  mixed 


TITANIUM  241 

with  30  c.c.  of  ferric  chloride  solution  (  =  4.8  g.  Fe)  and  the 
iron  removed  by  the  ether  separation.  The  titanium  was  pre- 
cipitated from  acetic  acid  solution  and  the  iron  titrated  by  the 
iodometric  method.  In  one  experiment  0.1007  g.  of  impure  TiO2 
were  obtained  and  the  iron  present  required  0.4  c.c.  of  tenth-nor- 
mal sodium  thiosulfate  solution,  corresponding  to  0.0032  g. 
Fe203.  The  corrected  weight  of  Ti02  was  thus  0.0975  g.  cor- 
responding to  0.0586  g.  Ti. 

In  a  similar  experiment  the  corresponding  values  were 
0.0993  g.  impure  TiO2,  0.2  c.c.  sodium  thiosulfate  =  0.0016  g. 
Fe2O3,  0.977  g.  pure  TiO2  and  0.0587  g.  Ti. 

Twenty  cubic  centimeters  of  the  titanium  solution  were  ti- 
trated with  ferric  chloride;  1  c.c.  of  FeCl3  =  0.004912  g.  Ti.  In 
duplicate  experiments  12.18  and  12.10  c.c.  of  the  ferric  chloride 
solution  were  used,  corresponding  to  0.0598  and  0.0594  g.  Ti. 

Thirty  cubic  centimeters  of  titanium  solution  were  mixed  with 
30  c.c.  of  ferric  chloride  solution,  the  iron  was  removed  by  ether, 
the  titanium  precipitated  as  dioxide,  and  the  titanium  deter- 
mined by  titration  in  the  hydrochloric  acid  solution  obtained 
after  fusing  the  impure  titanium  dioxide  with  sodium  carbonate. 
In  one  experiment  12.10  c.c.  and  in  another  12.05  c.c.  of  ferric 
chloride  solution  were  required,  corresponding  to  0.0594  and 
0.0592  g.  Ti. 

TITANIUM  DETERMINATIONS  BY  METHOD  2 

Duplicate  determinations  with  2-g.  samples  of  metallic  titan- 
ium using  one-fifth  of  the  solution  for  the  final  titration,  required 
respectively  50.5  and  50.7  c.c.  of  ferric  chloride  (1  c.c.  =  0.004995 
g.  Ti)  corresponding  to  63.0  and  63.3  per  cent  Ti. 

With  ferro-titanium  (Goldschmidt)  the  values  18.9  and  19.0 
per  cent  Ti  were  obtained  with  samples  weighing  1  g. 

In  a  sample  of  cast  iron,  the  titanium  was  determined  gravi- 
metrically,  simply  purifying  the  titanium  dioxide  by  heating 
with  sulfuric  and  hydrofluoric  acids  to  remove  silica.  The  values 
obtained  with  10-g.  samples  were  0.070  and  0.067  per  cent  Ti. 

ACCURACY  OF  THE  RESULTS  AND  PERMISSIBLE  DEVIATIONS 

Small  quantities  of  titanium  may  be  separated  from  iron  by  the 
ether  process  and  the  titanium  precipitated  as  dioxide.  The 

16 


242  CHEMICAL  ANALYSIS  OF  METALS 

volumetric  determination  of  small  quantities  of  titanium  is  nofc  at 
all  reliable  but  the  results  by  the  colorimetric  method  are  excel- 
lent. Results  should  agree  within  the  following  limits: 

PER  CENT  Ti  PERMISSIBLE  DEVIATION 

0.05-     0.2  ±0.02  per  cent 

0.2  1.0  ±0.03  per  cent 

1.0  5.0  ±0.1    percent 

5.0    -  10.0  ±0.2    percent 


CHAPTER  XVIII 
NITROGEN 

For  many  years  nitrogen  was  believed  to  play  an  important 
part  in  the  manufacture  of  steel.  This  view,  however,  has  been 
discredited1  and  the  determination  of  nitrogen  is  one  that  is  seldom 
included  in  the  chemical  examination  of  a  sample  of  steel.  Yet 
there  is  considerable  evidence  in  the  literature  that  the  small 
quantities  of  nitrogen  present  in  steel,  rarely  much  more  than  0.01 
per  cent,  may  have  considerable  influence  upon  the  value  of  the 
product.  As  a  rule,  nitrogen  produces  brittleness,  but  whether 
this  effect  is  produced  by  the  element  alone  or  only  in  conjunction 
with  sulfur  and  phosphorus  is  not  definitely  settled.  Stromeyer 
has  claimed  that  nitrogen  has  ten  times  more  effect  than  phos- 
phorus in  raising  the  tenacity  of  steel,  and  states  that  in  a  good 
specimen  of  steel  the  percentage  of  phosphorus  increased  by  five 
times  the  percentage  of  nitrogen  should  not  exceed  0.080  per 
cent.  Nitrogen  is  probably  present  in  steel  either  as  Fe5N2  or 
as  Fe4N2. 

1.  DETERMINATION     OF    NITROGEN    IN    STEEL 
METHOD  OF  A.  H.  ALLEN2 

Principle. — When  steel  is  dissolved  in  sulfuric  or  hydrochloric 
acid,  all  the  combined  nitrogen  is  obtained  in  the  form  of  ammo- 
nium salt.  If  the  solution  is  boiled  with  an  excess  of  sodium 
hydroxide,  ammonia  is  distilled  off  and  can  be  determined  by  the 
Nessler  test  or  by  absorption  in  a  measured  volume  of  standard 
acid  and  titrating  the  excess  of  the  latter  with  standard  alkali. 
The  quantity  of  nitrogen  present  is  so  small,  however,  that  it 

1  Fay,   Chem.  and  Met.  Eng.,   24,  289  (1921)   has  shown  recently  that 
nitrogen  causes  case  hardening  and  is  probably  an  important  factor  in 
cyanide  hardening. 

2  First  proposed  by  A.  H.  Allen  (J.  Iron  and  Steel  Institute,  1879,  480; 
1880,  181)  and  modified  by  J.  W.  Langley  (c/.  BLAIR'S  "Chemical  Analysis 
of  Iron  and  Steel"). 

243 


244  CHEMICAL  ANALYSIS  OF  METALS 

requires  a  large  sample  of  steel,  10  g.  at  least,  to  give  enough 
ammonia  to  determine  accurately  by  the  latter  method. 

Reagents  Required. — Distilled  Water  Free  from  Ammonia. — 
Add  a  little  potassium  permanganate  and  some  sodium  carbonate 
to  ordinary  distilled  water  and  redistil,  rejecting  the  first  fourth 
and  last  sixth  of  the  distillate. 

Standard  Ammonium  Chloride  Solution. — Dissolve  0.0382  g. 
of  pure  ammonium  chloride  in  1  liter  of  water  free  from  ammonia. 
One  cubic  centimeter  of  this  solution  is  equivalent  to  0.01  mg.  of 
nitrogen. 

Six-normal  Hydrochloric  Acid. — Half  fill  a  liter  flask  with 
concentrated  hydrochloric  acid.  Through  a  two-holed  rubber 
stopper,  which  fits  the  neck  of  the  flask,  insert  a  dropping  funnel 
and  a  gas  delivery  tube  connecting  the  flask  with  a  second  flask 
containing  pure  water,  free  from  ammonia.  Pour  some  pure, 
concentrated,  sulfuric  acid,  free  from  nitrous  acid,  into  the 
dropping  funnel  and  allow  this  to  flow  slowly  into  the  hydro- 
chloric acid,  heating  the  contents  of  the  flask  as  required.  Distil 
the  hydrochloric  acid  into  the  pure  water  until  the  density  of  the 
acid  solution  thus  formed  is  about  1.1. 

Sodium  Hydroxide  Solution. — Dissolve  300  g.  of  pure  caustic 
soda  in  500  c.c.  of  water  and  digest  it  24  hr.  with  a  copper-zinc 
couple.  To  make  the  couple,  cover  about  25  g.  of  thin  sheet 
zinc  with  a  fairly  concentrated  copper  sulfate  solution;  after 
about  10  min.  pour  off  the  solution  and  wash  the  residue  of 
copper  and  zinc  with  cold,  distilled  water. 

Nessler's  Reagent. — Dissolve  61.75  g.  of  pure  potassium  iodide 
in  250  c.c.  of  distilled  water  and  add  a  cold,  saturated  solution  of 
mercuric  chloride,  prepared  by  obtaining  a  hot,  saturated  solu- 
tion and  allowing  the  excess  of  the  salt  to  crystallize  out  on  cool- 
ing. Add  the  mercuric  chloride  solution  very  carefully,  stopping 
when  a  slight  permanent,  red  precipitate  of  mercuric  iodide, 
HgI2,  is  formed.  Dissolve  this  by  adding  0.75  g.  of  powdered 
potassium  iodide  and  then  add  150  g.  of  potassium  hydroxide 
dissolved  in  250  c.c.  of  water.  Make  up  to  a  liter  and  allow  it 
to  settle  over  night. 

Carefully  siphon  off  the  clear  solution  into  a  clean  bottle  and 
keep  it  in  a  dark  place.  This  solution  should  give  the  required 
color  within  5  min.  Nessler  solution  contains  the  complex  salt 


NITROGEN 


245 


K2[HgI4].  The  alkaline  solution  reacts  with  ammonia,  forming  a 
brown  precipitate,  or  a  coloration  varying  with  the  quantity  of 
ammonia  present;  the  reaction  is  expressed  by  the  following 
equation  : 


2K2[HgI4]  +  3KOH  +  NH4OH  =  0 


NH2.I 


+3H2O  +  7KI 


Procedure. — Place  30  c.c.  of  the  sodium  hydroxide  solution  in 
the  500-c.c.  Erlenmeyer  flask,  K,  Fig.  28  add  500  c.c.  of  water 
and  distil  until  a  50-c.c.  portion  of  the  distillate,  when  treated 


FIG.  28. 

with  1  c.c.  of  Nessler  reagent,  will  give  less  color  than  is  obtained 
with  1  c.c.  of  the  standard  ammonium  chloride  solution,  diluted 
to  50  c.c.  with  water  free  from  ammonia,  and  similarly  treated 
with  Nessler  reagent. 

Meanwhile  dissolve  3  g.  of  carefully  washed  steel  turnings  in 
30  c.c.  of  the  pure,  6-normal  hydrochloric  acid,  heating  if  neces- 
sary. Transfer  the  solution  to  the  bulb  of  the  dropping  funnel, 
T,  and,  when  the  solution  in  the  flask  is  boiled  free  from  ammonia, 
slowly  add  the  ferrous  chloride  solution.  Rotate  the  contents  of 
the  flask  to  make  sure  that  a  good  mixture  is  obtained  and  then 
carefully  continue  the  boiling.  When  about  50  c.c.  of  distillate  is 
obtained,  transfer  it  to  a  Nessler  tube,  which  is  merely  a  long, 
cylindrical  tube  of  uniform  bore,  mix  it  with  1  c.c.  of  Nessler 
reagent  and  allow  to  stand  5  min.  Compare  the  color  with 


246  CHEMICAL  ANALYSIS  OF  METALS 

that  obtained  with  1,  2,  3,  etc.,  c.c.  portions  of  standard  ammo- 
nium chloride  solution,  each  treated  with  1  c.c.  of  Nessler  reagent, 
diluted  to  50  c.c.  with  best  water  and  allowed  to  stand  5  min. 
Hold  the  tubes  side  by  side  in  a  slightly  inclined  position  and 
look  down  upon  them  with  a  background  of  white  paper.  The 
standards  should  be  prepared  at  the  same  time  the  test  is  being 
made.  Make  a  note  of  the  number  of  cubic  centimeters  of 
ammonium  chloride  solution  required  to  give  the  same  shade  as 
that  of  the  Nesslerized  distillate.  Continue  to  collect  portions  of 
the  distillate,  and  match  them  with  the  standards,  until  finally 
a  50-c.c.  portion  is  obtained  which  gives  a  distinctly  paler  color 
than  that  obtained  with  1  c.c.  of  the  standard. 

Computation. — If  n  represents  the  sum  of  the  number  of  cubic 
centimeters  of  standard  ammonium  chloride  solution  required  to 
match  the  various  portions  of  the  Nesslerized  distillate,  in  the 
analysis  of  a  sample  of  steel  weighing  s  g.,  then 

0.001  n 
per  cent  JN  =  - 

8 

2.  MODIFICATION  OF  L.  E.  BARTON1 

Dissolve  5  g.  of  the  steel  in  40  c.c.  of  ammonia-free  hydro- 
chloric acid  and  add  the  solution  to  the  distilling  flask  exactly 
as  in  the  above  directions.  Catch  the  distillate  in  a  graduated 
flask  and  distil  until  15.0  c.c.  of  distillate  are  obtained;  this  will 
contain  all  of  the  nitrogen,  as  experience  has  shown. 

Then  add  25  c.c.  of  the  standard  ammonium  chloride  solution 
to  the  contents  of  the  flask  and  distil  into  another  graduated 
flask  until  150  c.c.  of  distillate  are  obtained,  which  will  also 
contain  all  of  the  nitrogen  in  the  standard.  To  this  add  6  c.c.  of 
Nessler  reagent.  Since  the  standard  solution  contains  0 . 01  mg. 

25  V  0   Q1 

per    c.c.,   the   standard   distillate  will  now   contain  — 1-~ —  = 

loo 

0.0016  mg.  per  c.c.  A  single  standard  distillate  will  serve  for 
the  determination  of  nitrogen  in  several  samples  of  steel  if  the 
comparisons  are  being  made  at  the  same  time. 

For  the  color  comparison,  place  30  c.c.  of  the  distillate  from 
the  solution  of  the  steel  (=  1  g.  of  metal)  into  one  of  a  pair  of 

1  /.  Ind.  Eng.  Chem.,  6,  1012  (1914). 


NITROGEN  247 

Nessler  tubes,  add  1  c.c.  of  Nessler  reagent  and  allow  the  color  to 
develop  by  letting  the  solution  stand  5  min.  Into  the  other 
Nessler  tube  run  in  the  standard  distillate  until  the  colors  in  the 
two  Nessler  tubes  match,  making  the  final  comparison  after 
bringing  the  solutions  to  the  same  volume  by  the  addition  of  dis- 
tilled water  free  from  ammonia  to  one  or  the  other  of  the  tubes. 
Then  the  number  of  cubic  centimeters  of  standard  distillate  used 
multiplied  by  0. 0016  gives  the  percentage  of  nitrogen  in  the  steel. 
The  results  in  duplicate  determinations  by  this  method  do  not 
usually  differ  by  more  than  0.0005  per  cent  nitrogen.  The  aver- 
age nitrogen  content  of  steel  is  about  0.004  per  cent. 


CHAPTER  XIX 
OXYGEN 

Ingot  iron,  or  mild  steel,  often  contains  combined  oxygen. 
The  amount  of  oxides  present  depends  upon  the  extent  to  which 
decarburization  has  been  effected  by  oxidation  in  the  manufacture 
of  the  material. 

The  oxygen  is  present  chiefly  as  ferrous  oxide  dissolved  in  the 
crystals  of  ferrite  but  it  may  be  present  as  other  oxide  enclosed  in 
the  metal.  In  1882  Ledebur1  proposed  a  method  for  the  deter- 
mination of  oxygen  based  upon  the  reduction  of  the  oxide  at  a  red 
heat  by  hydrogen  and  weighing  the  water  thus  formed.  Ledebur's 
method  is  the  one  that  has-  been  used  most  for  the  determination 
of  oxygen  in  iron  and  steel  but  although  it  reduces  quantita- 
tively the  oxides  of  iron,  molybdenum,  tungsten,  etc.,  to  the 
metallic  state,  any  oxygen  combined  with  manganese,  aluminum, 
silicon,  titanium,  etc.,  escapes  the  determination,  or  at  least  for 
the  most  part.  In  1912,  W.  H.  Walker  and  W.  A.  Patrick2 
published  a  method  by  which  nearly  all  oxides  are  reduced.  The 
metal  is  heated  in  an  electric  vacuum  furnace  with  graphite  and 
the  carbon  monoxide  formed  is  determined. 

1.  LEDEBUR'S  METHOD 

To  obtain  accurate  results,  it  is  necessary  that  the  original 
material  be  perfectly  dry  and  free  from  organic  matter  and  that 
the  hydrogen  be  free  from  oxygen. 

Apparatus. — The  hydrogen  may  be  prepared  from  a  Finkener 
generator,3  a  Kipp  generator  or  by  the  electrolysis  of  dilute  sul- 

1  Stahl  u.  Eisen,  2,  193  (1882);  Leitfaden  fur  Eisenhiitten-Laboratorien,  p. 
105  (1900). 

2J.  Ind.  Eng.  Chem.,  4,  799  (1912);  8th  Intern.  Congr.  Appl.  Chem.,  21, 
139  (1912). 

3  Figure  29,  at  the  extreme  right. 

248 


OXYGEN 


249 


250  CHEMICAL  ANALYSIS  OF  METALS 

furic  acid.  The  gas  is  washed  to  remove  impurities1  and  then,  to 
remove  any  possibility  of  traces  of  oxygen  remaining,  it  is  passed 
through  a  hot  porcelain  tube  containing  platinized  asbestos. 
The  water  obtained  from  the  union  of  hydrogen  and  oxygen  in  this 
tube  is  removed  by  passing  the  gas  through  a  U-tube  containing 
phosphorus  pentoxide  between  plugs  of  glass  wool. 

The  thoroughly  purified  and  dried  gas  then  enters  the  porcelain 
combustion  tube  in  which  the  sample  is  to  be  heated  and  the 
water  formed  from  the  oxygen  in  the  sample  is  absorbed  in  a 
weighed  tube  containing  phosphorus  pentoxide.  To  prevent 
contamination  of  the  latter  from  moisture  in  the  atmosphere,  this 
last  absorption  tube  is  connected  with  a  bubble  tube  containing 
a  little  concentrated  sulfuric  acid;  this  tube  also  serves  to  indicate 
the  rate  at  which  the  gas  is  passing  through  the  apparatus. 

Procedure. — Special  pains  must  be  taken  with  the  sample  to  be 
used  in  this  determination.  To  remove  organic  substances  such 
as  oil  or  grease,  wash  the  borings  with  chloroform,  alcohol  and 
ether  using  reagents  which  are  free  from  non- volatile  residue. 
Select  borings  free  from  rust  or  scale,  unless  it  is  desired  to  de- 
termine the  oxygen  in  such  portions  of  the  metal.  Finally,  dry 
the  sample  by  heating  in  a  hot  closet  at  105°  and  cool  in  a 
desiccator. 

Before  starting  the  analysis  proper,  it  is  necessary  to  carry  out 
a  blank  experiment  with  the  apparatus  all  in  place  and  using  the 
same  procedure  as  in  the  analysis  itself;  this  is  to  make  sure  that 
there  is  no  gain  in  weight  in  the  phosphorus  pentoxide  tube  owing 
to  impurities  in  the  hydrogen,  to  leaky  apparatus,  or  to  moisture 
in  the  tube. 

Pass  a  current  of  hydrogen  through  the  entire  apparatus  with- 
out, at  first,  heating  either  of  the  porcelain  tubes.  After  30  or  45 
min.  collect  a  little  of  the  escaping  gas  in  a  test  tube  and  test  it 
to  see  if  it  will  burn  quietly.  If  this  is  the  case,  light  the  burners 
under  the  tube  containing  the  platinized  asbestos  and  keep  this 

1  In  Fig.  29,  the  purification  train  consists  of  a  tube  containing  50  per 
cent  caustic  potash  solution  (to  remove  HC1,  H^S,  etc.),  a  tube  containing 
alkaline  pyrogallol  solution  (about  3  per  cent  pyrogallol  in  10  per  cent 
caustic  potash:  this  serves  to  remove  oxygen)  and  a  tube  containing  con- 
centrated phosphoric  acid  (to  remove  most  of  the  moisture). 

Instead  of  pure  caustic  potash  solution,  Ledebur  recommends  a  solution 
of  lead  oxide  in  caustic  potash. 


OXYGEN  251 

tube  hot  as  long  as  a  continuous  stream  of  hydrogen  is  being 
passed  through  the  apparatus.  Detach  the  phosphorus  pentoxide 
tube,  allow  it  to  stand  near  the  balance  for  15  min.  and  weigh. 
Again  connect  this  tube  with  the  apparatus  and  heat  the  empty 
combustion  tube  to  redness  during  a  period  of  30  to  45  min. 
Then  turn  out  the  burners  under  this  tube  and  allow  it  to  cool 
while  the  current  of  hydrogen  is  still  passing.  Detach  the  absorp- 
tion tube,  allow  it  to  stand  at  least  15  min.  near  the  balance 
and  again  weigh  it.  If  this  second  weight  is  within  1  mg. 
of  the  first  weight,  the  apparatus  is  ready  for  the  combustion 
of  the  sample. 

Weigh  out  15  g.,  or  more,  of  the  metal  into  a  porcelain  boat.  If 
it  is  desired  to  use  a  larger  quantity  of  the  material,  weigh  it  upon 
a  watch-glass,  dry  in  a  closet  at  105°  for  an  hour,  cool  in  a  desicca- 
tor, and  weigh  again.  If  heating  for  half  an  hour  longer  causes 
no  further  loss  in  weight,  introduce  the  sample  into  the  combus- 
tion tube  which  has  already  been  heated  in  a  current  of  hydrogen. 
Large  samples  may  be  introduced  directly  into  the  combustion 
tube  between  plugs  of  ignited  asbestos.  Before  heating  or 
connecting  the  absorption  tube,  pass  the  hydrogen  through  the 
apparatus  for  an  hour  in  order  to  remove  all  traces  of  atmospheric 
oxygen.  Then  connect  the  weighed  absorption  tube  and  begin 
to  heat  the  tube  containing  the  sample.  Gradually  raise  the 
temperature  till  a  bright  red  heat  is  obtained  and  keep  the  tube 
at  this  temperature  for  about  30  min.,  then  turn  down  the 
flames  and  allow  the  furnace  to  cool.  Finally  detach  the  absorp- 
tion tube,  allow  it  to  stand  near  the  balance  for  at  least  15  min. 
and  weigh. 

After  the  furnace  has  cooled  down  with  the  hydrogen  still  pass- 
ing through  it,  the  oxidized  sample  can  be  removed  from  the  tube 
and  the  apparatus  is  ready  for  a  new  determination. 

Computation. — If  s  represents  the  weight  of  sample  taken  for 
analysis  and  p  the  weight  of  water  obtained  in  the  absorption 
tube,  then 

p  X  O  X  100  .» 

H2Q  x  g       =  88.81g   ==  Per  cent  oxygen 

Applicability  of  the  Method. — Besides  serving  for  the  determi- 
nation of  oxygen  in  iron,  the  method  can  be  used  with  a  fair  degree 
of  accuracy  for  determining  the  extent  to  which  a  sample  of  mate- 


252  CHEMICAL  ANALYSIS  OF  METALS 

rial  has  rusted  and  for  determining  the  amount  of  combined  oxy- 
gen in  samples  of  metallic  tungsten  or  molybdenum,  or  in  the 
alloys  of  these  elements  with  iron. 

Test  Analyses. — (1)  Determination  of  Oxygen  in  Mild  Steel. — 
Using  40-g.  samples  the  values  0.018  and  0.020  per  cent  O 
were  obtained  in  duplicate  determinations  with  one  sample  and 
the  values  0.016  and  0.015  per  cent  with  another. 

2.  Deter min  ation  of  Rust  on  Cast-iron  Borings. — The  borings  were 
composed  of  coarse  particles  and  of  very  fine  particles.     By  means 
of  sieves  the  borings  were  sorted  into  three  portions  according  to 
fineness.     Fifteen  grams  of  borings  gave  6.795  g.  of  finest  chips, 
4.747  g.  of  coarser  chips  and  3.456  g.  of  coarsest  chips.     Using 
these  proportions  of  the  material  the  values  2.60  and  2.50  per  cent 
O  were  obtained  by  combustion  of  a  15-g.  composite  sample. 

3.  Determination   of  the   Oxygen    Content  of  Ferro-tungsten. — 
Ten-gram  portions  of  the  dried  and  powdered  material  gave 
duplicate  results  of  0.056  and  0.050  per  cent  O. 

4.  Determination  of  the  Oxygen  Content  of  Powdered  Tungsten. — 
Duplicate  determinations  with  samples  weighing  about  30  g.  gave 
the  values  0.044  and  0.043  per  cent  O. 

5.  Oxygen  in  Metallic  Tungsten  and  in  Metallic  Molybdenum. — 
The  combustion  in  hydrogen  of  two  different  samples  of  tung- 
sten showed  0.46  and  0.52  per  cent  0  and  with  two  different 
samples  of  molybdenum  the  values  0.22  and  0.59  per  cent  O 
were  obtained;  10-g.  samples  were  used  in  each  case. 

2.  METHOD   OF  WM.  H.  WALKER  AND  W.  A.  PATRICK1 

Apparatus. — A  vacuum  furnace  of  the  Arsem  type  (Fig.  30) 
having  a  capacity  of  about  325  c.c.  capacity  is  recommended.2 
The  gun-metal  chamber  A  rests  inside  a  water  jacket  R.  The 
cover  B  is  fastened  to  the  chamber  by  means  of  18  cap-screws,  Z), 
and  the  joint  is  made  tight  by  a  rigid  lead  gasket.  The  tube,  J, 
through  which  the  furnace  is  exhausted,  is  soldered  into  the  cover. 
The  window  G  is  fastened  by  the  cover  to  six  cap-screws  and  the 
joint  is  made  tight  by  another  lead  washer.  The  mica  window  E 

1J.  Ind.  Eng.  Chem.,  4,  799  (1912);  Sth  Intern.  Congr.  Appl  Chem.,  21, 
139. 

2  General  Electric  Co.,  Schenectady,  N.  Y.,  cf.  J.  Am.  Chem.  Soc.,  28,  921 
(1906). 


OXYGEN 


253 


is  placed  in  the  top  of  the  window  tube.  The  brass  tubes  W, 
through  which  water  flows,  serve  as  electrodes.  Between  the 
electrodes  the  graphite  heater  L  is  fastened  by  means  of  clamps 
U.  The  crucible  containing  the  substance  is  supported  on  the 
stand  shown  in  the  drawing  and  is  thus  placed  in  the  hottest  part 
of  the  furnace. 

For  evacuating  the  furnace  a  small  rotary  oil  pump  in  series 
with  a  Geryk  pump1  works  satisfactorily  and  will  give  a  vacuum 


FIG.  30. 

of  0.01  mm.  in  less  than  15  min.  The  apparatus  for  collecting 
the  carbon  monoxide  is  shown  in  Fig.  31. 

Procedure. — Care  should  be  taken  in  preparing  the  sample  as 
described  on  p.  250.  Blank  determinations  should  also  be  made 
to  determine  the  quantity  of  carbon  monoxide  formed  when  no 
oxide  is  present;  and  in  every  analysis  allowance  must  be  made  for 
the  amount  of  carbon  monoxide  thus  obtained. 

1  To  be  obtained  from  any  large  dealer  in  scientific  apparatus. 


254 


CHEMICAL  ANALYSIS  OF  METALS 


For  the  analysis  itself,  weigh  20  to  25  g.  of  the  metal  into  a  small 
graphite  crucible  and  add  4  or  5  g.  of  powdered  graphite.  Place 
the  crucible  on  the  support  in  the  furnace  and  bolt  down  the 
cover  of  the  latter.  By  means  of  the  vacuum  pump,  thoroughly 
exhaust  the  furnace,  then  turn  on  the  cooling  water  and  heat 
the  furnace  to  about  500  to  600°  with  the  pump  still  running. 
This  is  necessary  to  withdraw  the  oxygen  absorbed  by  the 
heater  and  crucible.  As  carbon  does  not  begin  to  reduce  oxides 
below  900°  there  is  no  danger  in  heating  the  crucible  up  to  500°. 
After  heating  15  min.  at  this  temperature,  allow  the  crucible 


FIG.  31. 

to  cool,  which  it  does  very  rapidly  .  Introduce  nitrogen,  that  has 
been  dried  over  sulfuric  acid  and  phosphorus  pentoxide,  into  the 
cold  furnace  until  about  half  an  atmosphere  pressure  is  obtained. 
Again  evacuate  the  furnace  and  heat  gently  as  before.  Only  by 
such  treatment  is  it  possible  to  reduce  the  oxygen  left  in  the  tube 
to  a  reasonably  small  value. 

Now  turn  off  the  stopcock  leading  to  the  pump  and  apply 
70  volts  to  the  electrodes,  which  causes  a  current  of  about 
200  amperes  to  flow  through  the  heater.  A  high  temperature  is 
obtained  very  quickly  and  the  metal  usually  melts  within  3  or  4 


OXYGEN  255 

min.  Just  as  the  metal  melts  violent  ebullition  often  occurs. 
To  stop  this  open  the  circuit  for  a  short  time  and  allow  the  charge 
to  cool  somewhat.  When  the  metal  is  quiet  continue  the  heating 
for  20  min.  Then  cool  the  furnace  thoroughly  and  finally  fill  the 
furnace  to  atmospheric  pressure  with  nitrogen  that  has  been 
dried  over  sulfuric  acid  and  phosphorus  pentoxide. 

The  gas  now  in  the  furnace  is  analyzed  for  carbon  monoxide 
in  the  following  manner: 

Exhaust  the  vessel  C,  Fig.  31,  by  means  of  the  Toepler  pump, 
T,  and  connect  it  with  the  furnace  as  indicated  in  the  drawing. 
Open  the  stopcock  at  the  furnace  and  note,  by  means  of  the  dif- 
ferential gage  M,  the  difference  between  the  atmospheric  pressure 
and  the  pressure  within  the  furnace.  Open  the  stopcock  F  and 
fill  C  and  the  pump  T  with  gas  from  the  furnace.  A  decrease  in 
pressure  corresponding  to  the  volume  of  gas  withdrawn  from  the 
furnace  is  shown  by  the  gage  M .  In  this  way  it  is  easy  to  com- 
pute, without  errors  due  to  temperature  variation,  what  fraction 
of  the  original  volume  of  gas  in  the  furnace  is  used  for  the  analysis. 

Slowly  force  the  gas,  through  the  purifying  train  of  concen- 
trated sulfuric  acid,  solid  caustic  potash  and  solid  phosphorus 
pentoxide,  into  the  tube  containing  iodine  pentoxide  which  is 
heated  to  130°;  here  the  carbon  monoxide  is  oxidized  to  carbon 
dioxide  and  an  equivalent  quantity  of  iodine  is  liberated.  The 
iodine  is  absorbed  in  a  10  per  cent  solution  of  potassium  iodide  and 
finally  titrated  with  N/ 100  sodium  thiosulfate  solution. 

Computation. — If  n  c.c.  of  hundredth-normal  sodium  thiosul- 
fate solution  are  used  in  titrating  the  iodine  absorbed  in  the  analy- 
sis of  a  sample  weighing  s  g.  and  n\  represents  the  number  of 
c.c.  of  the  same  thiosulfate  used  in  a  blank  experiment,  then 

.  (n  -  nj  0.008 
N  -  -    =  per  cent  O 

NOTES. — In  all  cases  an  appreciable  quantity  of  iodine  is  obtained  in  a 
blank  experiment.  This  is  accounted  for  in  three  ways:  first,  a  practically 
constant  quantity  of  iodine  is  set  free  when  air  or  nitrogen  free  from  car- 
bon monoxide  is  led  over  hot  iodine  pentoxide;  second,  there  is  always  a 
little  absorbed  oxygen  retained  on  the  walls  and  in  the  heater  of  the  fur- 
nace; third,  a  trace  of  moisture  is  left  in  the  furnace  and  reacts  with  the  hot 
carbon.  By  keeping  the  temperature  of  the  iodine  pentoxide  at  130°  the 
oxidation  of  the  carbon  monoxide  is  complete  and  the  decomposition  of  the 


256 


CHEMICAL  ANALYSIS  OF  METALS 


iodine  pentoxide  is  reduced  to  a  minimum.  By  carefully  carrying  out  the 
analysis  as  outlined  above,  the  weight  of  oxygen  corresponding  to  a  blank 
determination  is  about  12  mg. 

Instead  of  using  the  Toepler  pump,  it  is  much  simpler  to  use  a  mer- 
cury aspirator,  replacing  the  reservoir  C  (Fig.  31)  by  a  liter  bottle  which  may 
be  filled  with  mercury.  It  is  then  easy  to  withdraw  a  known  fraction  of 
the  furnace  contents  and  to  force  it  through  the  iodine  pentoxide  tube. 

Although  the  results  obtained  by  the  method  are  not  as  accurate  as  might 
be  desired,  and  although  the  method  requires  a  complicated  apparatus  and 
careful  manipulation,  it  is  nevertheless  of  value  for  determining  the  pres- 
ence of  oxides  which  are  not  indicated  by  the  Ledebur  method  and  serves 
to  explain  the  discrepancies  often  noted  between  the  oxygen  content  as 
determined  by  that  method  and  the  physical  and  chemical  properties  of 
the  materials. 

TEST  ANALYSES 
1.    OXYGEN  FROM  FERRIC  OXIDE,  ALUMINA  AND   SILICA 

To  determine  the  accuracy  with  which  the  oxygen  of  a  sample 
of  iron  or  steel  will  be  converted  to  carbon  monoxide,  a  number 
of  analyses  were  made  using  an  iron  of  very  low  oxygen  content, 
and  adding  known  quantities  of  the  various  oxides  in  the  pure 
form.  In  addition  to  iron  oxide,  only  the  very  refractory  oxides 
of  aluminium  and  silicon  were  used;  other  more  easily  reducible 
oxides  such  as  manganese  and  copper  can  introduce  no  difficulties. 
The  weighed  amount  of  pure  oxide  together  with  a  known 
weight  of  iron  was  placed  in  the  graphite  crucible,  covered  with 
powdered  graphite  and  heated  as  described.  The  following 
results  were  obtained: 


Weight 
of  oxide 

Oxygen 
calculated 

Oxygen 
found 

Ferric  oxide 

0  5650 

0  1695 

0  1700 

Ferric  oxide 

0  6525 

0  1960 

0  1940 

Ferric  oxide  
Ferric  oxide  
Alumina 

0.8400 
0.1516 
0  4925 

0.2520 
0.0455 
0  2310 

0.2440 
0.0480 
0  2040 

Alumina 

0  1860 

0  0875 

0  0810 

Alumina          .                  

0.3065 

0.1440 

0.1260 

Silica                                         

0.0673 

0.0360 

0.0342 

Silica  

0.0320 

0.0181 

0.0171 

OXYGEN 


257 


2.  COMPARATIVE  RESULTS  BY  THE  LEDEBUR  AND  WALKER- 
PATRICK  METHODS 

Sample  No.  1  was  a  special  heat  of  open-hearth  steel  to  which 
iron  ore  and  an  excess  of  manganese  were  added  in  the  ladle. 
The  finished  steel  gave  evidence  of  having  a  high  oxygen  content. 
Number  2  was  a  high-grade,  open-hearth  steel.  Number  3  was 
also  an  open-hearth  steel  and  No.  4  was  the  same  as  No.  3  but 
from  an  ingot  to  which  ore  was  added.  Numbers  7  and  8  were 
samples  of  open-hearth  steel  and  Nos.  9  and  10  were  open-hearth 
iron.  Numbers  Ha  and  116  were  duplicate  analyses  of  an  ingot 
iron  of  early  manufacture  and  Nos.  12a  and  126  were  duplicate 
analyses  of  ingot  iron  of  later  make. 


Per  cent 

Per  cent 

No. 

Per  cent 

Per  cent 

Per  cent 

Per  cent 

Per  cent 

Per  cent 

0, 

o, 

C 

Mn 

S 

P 

Si 

Cu 

Ledebur 

Walker- 

Patrick 

1 

0.19 

0.92 

0.052 

0.123 

0.006 

0.290 

2 

0.000 

0.090 

3 

0.17 

0.65 

0.097 

0.064 

0.017 

0.110 

4 

0.12 

0.17 

0.065 

0.088 

0.015 



0.330 

5 

0.09 

0.18 

0.061 

0.087 

0.019 

0.310 

6 

0.14 

0.24 

0.070 

0.092 

0.009 

..... 

0.065 

7 

0.09 

0.33 

0.065 

0.068 

0.006 

0.17 

0.009 

0.021 

8 

0.08 

0.33 

0.036 

0.070 

0.005 

0.22 

0.010 

0.039 

9 

0.01 

0.03 

0.050 

0.007 

0.003 

0.20 

0.037 

0.056 

10 

0.01 

0.04 

0.015 

0.008 

0.004 

0.19 

0.052 

0.064 

lla 

0.01 

trace 

0.015 

0.002 

0.069 

0.230 

lib 

0.01 

trace 

0.015 

0.002 

0.076 

0.210 

12o 

0.02 

0.03 

0.029 

0.004 

0.0014 

0.043 

0.100 

126 

0.02 

0.03 

0.029 

0.004 

0.0014 

0.043 

0.110 

17 


CHAPTER  XX 
ZIRCONIUM 

Small  quantities  of  zirconium  are  sometimes  present  in  steel. 
Chemists  at  the  Bureau  of  Standards  have  studied  the  various 
methods  which  have  been  proposed  for  the  estimation  of  zirco- 
nium and  published  a  procedure  for  the  determination  of  silicon, 
aluminium,  titanium  and  zirconium  in  the  presence  of  other 
alloying  metals  such  as  possibly  tungsten,  chromium,  vanadium, 
phosphorus,  molybdenum,  copper,  nickel,  uranium  and  cerium.1 

Procedure.  —  Dissolve  5  g.  of  steel  in  50  c.c.  of  12-normal  hydro- 
chloric acid,  heating  gently  and  adding  nitric  acid  in  small 
portions  from  time  to  time  until  the  iron  is  all  oxidized  to  the 
ferric  state.2  Evaporate  the  solution  to  dryness,  moisten  the 
residue  with  10  c.c.  of  concentrated  hydrochloric  acid  and  repeat 
the  evaporation,  this  time  baking  the  residue  somewhat  to 
decompose  any  nitrates  that  may  remain.  Take  up  the  residue 
in  50  c.c.  of  6-normal  hydrochloric  acid  and  heat  until  all  the 
basic  ferric  chloride  is  dissolved.  Filter,  wash  the  impure  silicic 
acid  with  hot  3  per  cent  hydrochloric  acid,  and  save  the  nitrate. 

Ignite  the  impure  silica  and  determine  its  purity  by  hydro- 
fluoric acid  treatment  as  described  on  page  118.  Fuse  the 
slight  residue  with  a  small  quantity  of  potassium  pyrosulfate,3 
dissolve  the  melt  in  15  c.c.  of  5  per  cent  sulfuric  acid  and  add 
this  solution  to  the  acid  extract  from  the  ether  separation, 
obtained  as  follows: 

Evaporate  the  nitrate  and  washings  from  the  silica  determi- 
nation to  sirupy  consistency,  take  up  in  40  c.c.  of  6-normal 
hydrochloric  acid  and  extract  with  ether  as  described  on  p. 


and  KNOWLES,  J.  1.  E.  C.,  12,  562  (1920). 

2  About    8  c.c.   of    concentrated  nitric  acid  should   be  added  in   1-c.c. 
portions. 

3  Potassium  acid  sulfate  fused  until  all  the  hydrogen  is  expelled  as  water 
and  fumes  of  sulfuric  anhydride  begin  to  escape. 

258 


ZIRCONIUM  259 

73.  The  acid  extract  will  contain  a  little  iron  and  all  of  the 
zirconium,  titanium,  aluminium,  manganese,  chromium,  copper, 
etc.  The  ether  extract  will  contain  the  greater  part  of  the  iron 
and  most  of  the  molybdenum;  it  is  discarded. 

Boil  off  the  ether  in  the  acid  extract,  add  the  sulfuric  acid 
solution  obtained  in  the  purification  of  the  silica  and  a  little 
concentrated  nitric  acid  (about  0.5  c.c.)  to  make  certain  that 
all  the  iron  is  in  the  ferric  condition.  Dilute  to  300  c.c.,  cool, 
and  precipitate  with  20  per  cent  sodium  hydroxide  solution, 
adding  10  c.c.  in  excess.  This  serves  to  precipitate  the  remainder 
of  the  iron  together  with  all  the  zirconium  and  titanium.  The 
sodium  hydroxide  solution  should  be  as  pure  as  possible  and  free 
from  carbonate.  Dissolve  the  precipitate  in  hot,  6-normal 
hydrochloric  acid,  repeat  the  sodium  hydroxide  precipitation 
and  combine  the  two  nitrates  and  use  them  for  the  determination 
of  aluminium.  Dissolve  the  precipitate  in  hot  6-normal  hydro- 
chloric acid  and  use  the  resulting  solution  for  the  determination 
of  titanium  and  zirconium.  Inasmuch  as  zirconium  phosphate 
is  difficultly  soluble  in  hydrochloric  acid,  some  zirconium  may  be 
left  on  the  last  filter.  To  recover  it,  ignite  the  filter,  fuse  the  ash 
with  sodium  carbonate  and  dissolve  out  the  sodium  salts  from  the 
cold  melt  by  treatment  with  hot  water.  Discard  the  aqueous 
extract  and  dissolve  the  residue  in  hot  6-normal  hydrochloric  acid, 
adding  the  solution  to  that  containing  the  greater  part  of  the 
zirconium. 

Determination  of  Aluminium. — (a)  In  the  Absence  of  Chromium 
and  Uranium. — Add  a  few  drops  of  methyl  red  to  the  sodium 
hydroxide  solution,  neutralize  with  hydrochloric  acid  and  add  in 
excess  4  c.c.  of  concentrated  hydrochloric  acid  per  100  c.c.  of 
solution,  boil,  make  barely  alkaline  with  ammonium  hydroxide, 
continue  boiling  for  3  min.  and  set  aside  for  10  min.  If  no 
precipitate  forms  the  absence  of  aluminium  is  assured.  If  a 
precipitate  is  obtained,  filter  it  off,  and  discard  the  filtrate. 
Without  washing  the  precipitate,  dissolve  it  in  hot  6-normal 
hydrochloric  acid,  using  as  little  as  possible.  Dilute  to  50  c.c., 
neutralize  with  ammonium  hydroxide  and  add  2  c.c.  of  concen- 
trated nitric  acid.  Heat  to  50°  and  precipitate  phosphorus  with 
ammonium  molybdate  in  the  usual  manner.  Filter  and  wash 
with  ammonium  acid  sulfate  solution  as  described  on  p.  107  and 


260  CHEMICAL  ANALYSIS  OF  METALS 

discard  the  precipitate.  Precipitate  the  aluminium  in  the  filtrate 
by  ammonium  hydroxide  as  directed  above.  Filter,  and  discard 
the  filtrate  without  washing,  dissolve  the  precipitate  in  a  little 
hot,  3-normal  hydrochloric  acid  and  reprecipitate  with  ammonium 
hydroxide.  Filter,  wash  the  aluminium  hydroxide  precipitate  a 
few  times  with  2  per  cent  ammonium  chloride  solution,  ignite  in 
a  platinum  crucible  and  weigh  as  A12O3.  Inasmuch  as  this 
precipitate  will  always  contain  a  little  silica  from  the  action  of 
caustic  alkali  on  glass,  it  should  be  treated  with  sulfuric  and 
hydrofluoric  acids  to  volatilize  silicon  fluoride  and  it  is  advisable 
to  run  a  blank  determination  with  the  same  quantities  of  reagents 
as  used  in  the  regular  analysis;  when  a  correction  factor  is  made 
in  this  way  it  is  unnecessary  to  apply  the  hydrofluoric  acid 
correction  provided  the  alkali  solutions  do  not  stand  an  abnormal 
time  in  contact  with  glass.  The  silica  and  alumina  content  of 
a  solution  of  sodium  hydroxide  kept  in  glass  will  increase  from 
day  to  day. 

(b)  In  Steels  Containing  Chromium. — Proceed  as  above  until 
the  filtrate  from  the  ammonium  phosphomolybdate  precipitate 
is    obtained.     Then    make    the    solution    ammoniacal,    oxidize 
with  a  little  bromine  water,1  make  just  acid  with  nitric  acid, 
add  ammonium  hydroxide  in  slight  excess  and  treat  the  alu- 
minium hydroxide  precipitate  as  described  above. 

(c)  In  Steels  Containing    Uranium. — The   only  modification 
required  is  the  substitution  of  ammonium  carbonate  for  ammo- 
nium   hydroxide    as   the    final    precipitant    of   the    aluminium 
hydroxide. 

(d)  In  Steels  Containing  Vanadium. — Aluminium  hydroxide, 
as  obtained  by  the  above  procedures  from  steels  containing 
vanadium  is  contaminated  by  this  element.     When  dealing  with 
these  steels  proceed  as  follows:  Fuse  the  weighed  A1203  residue 
with  potassium  pyrosulfate,  extract  the  cooled  melt  with  5  per 
cent  sulfuric  acid,  reduce  the  vanadium  in  a  Jones  reductor 
having  ferric  alum  in  the  receiver  and  titrate  the  reduced  solu- 
tion with  standard  permanganate.     The  zinc  reduces  the  vana- 
dium to  the  bivalent  condition  and  the  ferric  ions  oxidize  it  back 

1  This  oxidation  of  chromium  by  bromine  in  ammoniacal  solution  is  the 
weak  part  of  the  method  because  the  bromine  reacts  with  ammonium  ions 
to  form  nitrogen  and  the  solution  tends  to  become  acid  (c/.  p.  79). 


ZIRCONIUM  261 

to  the  quinquevalent  state  leaving  an  equivalent  quantity  of 
ferrous  ions  to  titrate  with  permanganate.  One  cubic  centimeter 
of  tenth-normal  KMn04  =  0.00607  g.  V2O5.  Subtract  the  weight 
of  V2Os  from  that  of  the  greater  impure  A12O3  precipitate. 

Determination  of  Zirconium  and  Titanium. — Dilute  the  hydro- 
chloric acid  solution  to  250  c.c.,  neutralize  with  ammonium 
hydroxide  so  as  to  leave  approximately  5  per  cent  (by  volume)  of 
hydrochloric  acid,  add  2  g.  of  tartaric  acid,  and  treat  with  hydro- 
gen sulfide  until  the  iron  has  been  reduced.  Filter  if  the  sulfide 
group  is  indicated.  Make  the  hydrogen  sulfide  solution  ammo- 
niacal  and  continue  the  addition  of  the  gas  for  5  min.  Filter  care- 
fully and  wash  with  dilute  ammonium  sulfide-ammonium  chloride 
solution.  Filter  through  a  new  filter  if  the  presence  of  iron 
sulfide  in  the  filtrate  is  indicated.  Save  the  filtrate. 

(The  precipitate  contains  sulfides  of  iron,  manganese 
nickel  and  cobalt  if  these  elements  are  present  in  the  steel. 
It  is  preferable  to  determine  these  in  separate  portions  of  the 
steel.) 

Neutralize  the  ammonium  sulfide  filtrate  with  sulfuric  acid, 
add  30  c.c.  in  excess  and  dilute  with  water  to  300  c.c.  Digest  on 
the  steam  bath  until  sulfur  and  sulfides  have  coagulated,  filter, 
wash  with  100  c.c.  of  10  per  cent  sulfuric  acid,  and  cool  the  filtrate 
in  ice  water. 

Add  slowly  and  with  stirring  an  excess  of  a  cold  6  per  cent 
water  solution  of  cupferron.1  (The  presence  of  an  excess  is 
shown  by  the  appearance  of  a  white  cloud  which  disappears, 
instead  of  forming,  a  permanent  coagulated  precipitate.)  After 
10  min.  filter  on  paper,  using  a  cone  and  very  gentle  suction,  and 
wash  the  precipitate  thoroughly  with  cold  10  per  cent  hydro- 
chloric acid. 

Carefully  ignite  in  a  tared  platinum  crucible,  completing  the 
ignition  over  a  blast  lamp  or  large  Meker  burner,  cool,  and  weigh 
the  combined  zirconium  and  titanium  oxides  (ZrO2  +  TiO2). 

Fuse  with  potassium  pyrosulfate,  dissolve  in  50  c.c.  of  10  per 
cent  (by  volume)  sulfuric  acid  and  determine  titanium  colori- 
metrically  or  volumetrically.  Calculate  titanium  oxide,  sub- 
tract the  weight  found  from  that  of  the  combined  oxides,  and 
calculate  zirconium. 

1  The  ammonium  salt  of  phenyl-nitroso-hydroxylamine. 


262  CHEMICAL  ANALYSIS  OF  METALS 

(c)    Notes   on   this   Method 

1.  Phosphorus  pentoxide  contaminates  the  precipitate  to  so 
slight  an  extent  that  it  can  be  disregarded. 

2.  Vanadium    interferes  no  matter  what  its  valency.     The 
interference  is  not  quantitative.     If  present  in  the  steel,  proceed 
as  usual  through  the  weighing  of  the  cupferron  precipitate.     Then 
fuse  thoroughly  with  sodium  carbonate,  cool,  extract  with  water, 
filter,   and  determine  the  vanadium  in  the  nitrate  by  adding 
sulfuric  acid,  reducing  through  a  Jones  reductor  into  a  solution 
of  ferric  alum-phosphoric  acid  (see  p.  109)  and  then  titrating 
with   standard  permanganate.     Vanadium  is  thus  reduced  to 
V2O2  and  then  oxidized  to  V205.     Calculate  to  V205  and  subtract 
from  the  combined  oxides.     Ignite  in  the  original  crucible  the 
residue  insoluble  in  water,  fuse  with  potassium  pyrosulfate  and 
proceed  as  directed  for  titanium. 

3.  Tungsten  does    not  interfere  since  it  is  separated    from 
zirconium  and   titanium  by  the  sodium  hydroxide  treatment, 
and  from  aluminium  by  the  ammonium  hydroxide  precipitation. 
If  tungsten  is  present  in  large  amount  it  may  be  found  desirable 
to  fuse  the  non-volatile  residue  from  the  silicon  determination 
with  sodium  carbonate,  extract  with  water,  filter,  dissolve  the 
residue  in  hot  1  : 1  hydrochloric  acid,  and  add  to  the  acid  extract 
from  the  ether  separation. 

4.  Uranium  is   partially  carried  down  when  present  in  the 
quadrivalent  condition,   but  not  at  all  in  the  sexivalent  state. 
If  this  element  is  suspected,  boil  out  all  hydrogen  sulfide  before 
the   cupferron   precipitation,   oxidize   with   permanganate   to  a 
faint  pink,  cool,  and  proceed  with  the  cupferron  precipitation. 

5.  Thorium  and  cerium  interfere,  but  they  are  not  thrown 
down  quantitatively.     In  case  these  elements  are  suspected,  the 
oxidized  solution  used  for  the  titanium  determination  must  be 
quantitatively  preserved  and  reduced  with  a  little  sulfurous  acid. 
The  rare  earths  are  then  separated  by  Hillebrand's  method1 
as  follows:     Precipitate  the  hydroxides  with  an  excess  of  potas- 
sium hydroxide,  decant  the  liquid,  wash  with  water  once  or 
twice  by  decantation  and  then  slightly  on  the  filter.     Wash 
the  precipitate  from  the  paper  into  a  small  platinum  dish,  treat 

1  U.  S.  Geol.  Survey,  Bulletin  700,  176. 


ZIRCONIUM  263 

with  hydrofluoric  acid,  and  evaporate  nearly  to  dryness.  Take 
up  in  5  c.c.  of  5  per  cent  (by  volume)  hydrofluoric  acid.  If  no 
precipitate  is  visible,  rare  earths  are  absent.  If  a  precipitate  is 
present,  collect  it  on  a  small  filter  held  by  a  perforated  platinum 
or  rubber  cone  and  wash  it  with  from  5  to  10  c.c.  of  the  same  acid. 
Wash  the  crude  rare-earth  fluorides  into  a  small  platinum  dish, 
burn  the  paper  in  platinum,  add  the  ash  to  the  fluorides  and 
evaporate  to  dryness  with  a  little  sulfuric  acid.  Dissolve  the 
sulfates  in  dilute  hydrochloric  acid,  precipitate  the  rare-earth 
hydroxides  by  ammonia,  filter,  redissolve  in  hydrochloric  acid, 
evaporate  the  solution  to  dryness  and  treat  the  residue  with  5  c.c. 
of  boiling-hot,  5  per  cent  oxalic  acid.  Filter  after  15  min.,  collect 
the  oxalates  on  a  small  filter,  wash  with  not  more  than  20  c.c.  of 
cold  5  per  cent  oxalic  acid,  ignite  and  weigh  as  rare-earth  oxides 
which  are  to  be  deducted  from  the  weight  of  the  cupferron 
precipitate. 

The  above  procedure  does  not  give  an  absolutely  quantitative 
recovery  of  the  rare  earths.  Experiments  indicate  a  recovery 
of  approximately  85  per  cent  of  the  rare  earths  present  in  residues 
containing  100  mg.  of  zirconia,  2  mg.  of  thoria,  and  2  mg.  of  ceria. 


CHAPTER  XXI 

ELECTROMETRIC  METHODS  APPLICABLE  TO  STEEL 
ANALYSIS 

The  electrometric  methods  to  be  described  here  depend  upon 
the  measurement  of  differences  in  potential  or,  as  in  the  case  of 
carbon,  upon  the  measurement  of  electrical  resistivity.  Although 
the  theoretical  principles  involved  are  those  of  the  electrolytic 
cell  and  are  utilized  in  electrolytic  separations  with  graded 
cathode  potential,  the  development  of  this  type  of  analysis,  in 
which  a  quantitative  estimation  of  a  substance  is  based  wholly 
upon  an  electrical  measurement,  has  taken  place  for  the  most 
part  since  1900  and  such  methods  have  only  been  applied  to  the 
analysis  of  iron  and  steel  since  1915.  For  this  reason  it  seems 
desirable  here  to  discuss  the  electrolytic  theory  at  some  length 
and  without  assuming  that  the  reader  knows  much  about  elec- 
tricity or  electrical  units. 

Electricity  like  all  other  forms  of  energy  may  be  resolved  into 
two  factors — an  intensity  factor  called  electromotive  force  which 
is  measured  in  volts  and  depends  upon  a  difference  in  potential, 
and  a  capacity  factor  representing  the  quantity  of  electricity, 
which  is  measured  in  coulombs.  It  is  customary  to  liken  the 
flow  of  electricity  to  that  of  a  body  of  water;  the  energy  of  flowing 
water  depends  upon  the  intensity  factor  or  head  and  upon  the 
quantity  of  water  which  flows.  The  energy  in  either  case  is 
measured  by  the  product  of  these  two  factors. 

Just  as  water  in  flowing  has  more  or  less  resistance  to  overcome, 
so  the  rate  at  which  electricity  flows  is  determined  in  part  by  the 
resistance  to  be  overcome  as  well  as  by  the  factors  of  the  energy 
itself. 

In  1827,  G.  S.  Ohm  enunciated  his  well-known  law:  The 
strength  of  current  flowing  in  a  conductor  is  directly  proportional 
to  the  difference  in  potential  between  the  ends  of  the  conductor  arid 
inversely  proportional  to  the  resistance.  If  i  represents  the  strength 

264 


ELECTROMETRIC  METHODS  265 

of  current,  E  the  electromotive  force  or  difference  in  potential, 
and  R  the  resistance,  Ohm's  law  may  be  formulated, 


The  unit  for  measuring  the  strength  of  current  is  the  ampere,  that 
of  electromotive  force  is  the  volt  and  that  of  resistance  is  the 
ohm.  In  terms  of  these  units,  Ohm's  law  reads 

volts 

amperes  =  -7— 
ohms 

The  ohm  is  denned  as  the  resistance  at  0°C.  of  a  column  of 
mercury  106.3  cm.  long  and  1  sq.  mm.  in  cross  section.  The  am- 
pere is  the  current  that  will  cause  the  deposition  of  1.1118  mg. 
of  silver  in  1  sec.  from  a  solution  of  silver  nitrate.  The  volt  is  the 
electromotive  force  necessary  to  drive  a  current  of  1  ampere 
through  a  resistance  of  1  ohm.  The  coulomb  is  defined  as  the 
current  corresponding  to  the  flow  of  1  ampere  in  1  second.  The 
energy  of  the  electric  current,  or  the  power,  is  determined  by 
multiplying  coulombs  X  volts.  This  unit  of  electricity  is  often 
called  the  watt-second  but  it  might  just  as  well  be  called  a  coulomb- 
volt.  A  watt-second  is  also  called  a  joule]  it  is  equivalent  to  10 
million  ergs  or  to  0.2382  calories  of  heat  energy. 

From  these  elementary  units  other  units  such  as  milli-ampere, 
milli-volt,  watt-hour,  kilowatt-hour  and  kilowatt-year  are  derived 
and  have  the  meanings  indicated  by  their  names.  Another 
important  unit  is  the  so-called  electrochemical  equivalent, 
Faraday  or  farad.  It  signifies  96,500  coulombs  or  26.81  ampere- 
hours  and  represents  the  quantity  of  electricity  required  to  dis- 
charge the  weight  in  grams  of  any  univalent  ion  or  radical.  Thus 
if  hydrochloric  acid  is  decomposed  by  electrolysis  in  such  a  way 
that  all  of  the  current  is  used  for  hydrogen  at  the  cathode  and 
chlorine  at  the  anode,  the  passage  of  one  Faraday  of  electricity 
will  cause  the  discharge  of  1  g.  of  hydrogen  and  35.5  g.  of  chlo- 
rine. If  1  gram-molecular  weight  of  hydrochloric  acid  is  com- 
pletely ionized  in  aqueous  solution,  the  charges  represented  as 
residing  upon  the  hydrogen  ions  and  the  chlorine  ions  correspond 
to  96,500  coulombs  of  electricity. 

Ions  of  different  metals  hold  their  charges  with  different 
degrees  of  tenacity.  Ions  with  strong  electro-affinity  are  harder 


266  CHEMICAL  ANALYSIS  OF  METALS 

to  discharge  than  those  with  weak  electro-affinity;  it  requires 
more  voltage  to  discharge  the  former  although  the  quantity  of 
electricity  involved  is  determined  simply  by  the  valence  of  the 
ion.  If  a  free  element  is  placed  in  contact  with  the  ions  of  a 
metal  of  weaker  electro-affinity,  the  charge  on  the  latter  passes 
to  the  former;  thus  placing  zinc  in  copper  sulfate  solution  causes 
zinc  to  dissolve  and  copper  to  precipitate, 

Cu++  +  Zn-+Cu  +  Zn++  (1) 

This  is  known  to  all  chemists  but  often  too  little  emphasis  is 
placed  upon  the  fact  that  reactions  of  this  type  are  to  some 
extent  reversible.  The  more  copper  ions  and  the  fewer  zinc 
ions  present,  the  easier  it  is  for  the  copper  to  be  deposited  and 
for  the  zinc  to  dissolve.  As  the  reaction  progresses  it  slows  down, 
although  in  this  particular  case  the  reaction  appears  to  take 
place  until  all  the  copper  is  precipitated  because  there  is  so  much 
difference  in  the  electro-affinities  of  these  two  metals. 

The  elements,  especially  the  metals,  are  often  classified  with 
respect  to  their  electrochemical  affinities.  The  more  common 
metals  are  arranged  in  the  following  order:  K,  Na,  Be,  Sr,  Ca, 
Mg,  Al,  Cr,  Mn,  Zn,  Cd,  Fd,  Co,  Ni,  Sn,  Pb,  H,  Sb,  Bi,  As,  Cu, 
Hg,  Ag,  Pt,  Au.  In  general,  a  metal  placed  in  contact  with  ions 
of  a  metal  which  comes  after  it  in  this  series  will  dissolve  and  the 
original  ions  will  be  precipitated  as  free  metal;  there  are  many 
apparent  exceptions  to  this  rule  because  other  factors  other  than 
relative  electro-affinities  come  into  consideration. 

The  tendency  for  zinc  to  dissolve  when  placed  in  copper 
sulfate  solution  is  often  explained  by  saying  that  zinc  has  a 
greater  electrolytic  solution  pressure  than  copper.  This  electro- 
lytic solution  pressure,  or  tendency  of  the  metal  to  pass  into  solu- 
tion as  positively  charged  ions,  cannot  be  measured  directly  but 
its  theoretical  value  can  be  computed.  The  table  of  electro- 
affinities  is  often  called  the  table  of  electrolytic  solution  tensions. 
In  other  words,  electro-affinity  and  electrolytic  solution  tension 
are  equivalent  theoretical  forces  used  to  explain  the  same  phe- 
nomena; the  element  which  has  the  greatest  solution  tension 
naturally  is  the  one  which  holds  on  to  the  electric  charge  with 
greatest  tenacity -after  the  ions  are  once  formed. 

Again,  if  we  define  oxidation  as  the  process  of  adding  positive 


ELECTROMETRIC  METHODS  267 

charges  or  removing  negative  charges  from  a  metal  or  ion,  it  is 
clear  that  in  equation  (1)  zinc  is  oxidized  and  copper  is  reduced 
and  another  way  of  explaining  the  reaction  is  to  say  that  zinc  has 
a  greater  reduction  potential  than  copper.  The  electro-chemical 
series,  therefore,  may  also  be  called  the  series  of  normal  reduc- 
tion potentials  or,  more  briefly,  the  voltage  series  of  the  elements. 
Moreover,  the  tendency  of  any  equation  of  oxidation  and  reduc- 
tion reaction  to  take  place  may  be  measured  in  terms  of  voltage 
and  the  ions  concerned  may  be  assigned  a  place  in  the  table; 
for  example,  the  tendency  of  ferrous  ions  to  become  ferric  ions  is 
about  the  same  as  that  of  metallic  copper  to  form  cupric  ions 
and  zinc  will  reduce  ferric  ions  just  about  as  readily  as  it  will 
precipitate  copper. 

When  zinc  is  placed  in  copper  sulfate  solution,  equation  (1), 
it  is  clear  that  a  flow  of  electricity  takes  place  and  it  is  possible 
to  utilize  this  current  as  in  the  Daniell  cell  in  which  a  strip  of 
zinc  is  placed  in  zinc  sulfate  solution  and  a  strip  of  copper  is 
placed  in  copper  sulfate  solutions;  the  two  metals  are  connected 
externally  with  a  wire  and  the  two  solutions  are  in  electrical 
contact,  being  separated  only  in  some  such  way  as  by  a  porous 
wall  which  serves  to  hinder  diffusion.  If  the  copper  sulfate 
solution  is  kept  away  from  the  strip  of  zinc,  no  chemical  reaction 
takes  place  until  the  two  metals  are  connected  by  the  wire. 
The  conventional  way  of  expressing  the  flow  of  current  in  this 
cell  is  as  follows: 

In  the  external  circuit 


Zn/ZnSO4/CuS04/Cu 

In  the  solution 

The  arrow  shows  the  positive  to  negative  direction  of  the  cur- 
rent.1 

1  The  modern  electron  theory  is  based  on  the  assumption  that  the  flow 
of  electricity  is  really  due  to  the  movement  of  negatively-charged  electrons 
so  that  the  current  really  flows  in  the  negative  to  positive  direction.  The 
chemist  sometimes  thinks  of  the  positively-charged  ions  passing  from  the  zinc 
to  the  copper  in  the  solution  but  the  physicist  thinks  first  of  the  positive 
charges  passing  from  the  copper  to  the  zinc  on  the  wire.  The  chemist 
thinks  of  zinc  as  positive  because  it  forms  ions  with  a  positive  charge;  the 
physicist  remembers  that  the  metal  is  left  negative  when  the  solution  becomes 
positive.  Both  points  of  view  are  correct  but  are  confusing  to  the  beginner. 


268  CHEMICAL  ANALYSIS  OF  METALS 

When  zinc  dissolves  in  the  Daniell  cell  it  has  to  overcome  a 
certain  resistance  which  increases  with  the  concentration  of  the 
zinc  ions  already  in  solution;  the  pressure  exerted  by  dissolved 
ions  is  called  osmotic  pressure  and  tends  to  neutralize  the  electro- 
lytic solution  pressure.  Nernst,  with  the  aid  of  integral  calculus, 
has  computed  the  electromotive  force,  E,  which  results  when  a 
metal  of  P  electrolytic  solution  pressure  is  placed  in  contact 
with  a  solution  of  its  own  ions  having  the  osmotic  pressure  P. 
If  R  represents  the  gas  constant  of  the  well-known  expression 
pv  =  nHT  expressed  here  in  volts  X  coulombs,  T  the  absolute 
temperature,  F  the  electrochemical  equivalent,  and  n  the  valence 
of  the  ions,  the  Nernst  formula  reads: 

RT  i       P  ™ 

E==^loge-  (2) 

It  is  important  to  note  that  the  observed  electromotive  force, 
or  voltage  E,  varies  with  the  temperature,  concentration  of  the 
solution  (which  determines  the  osmotic  pressure),  and  with  the 
valence  of  the  ions.  R,  the  gas  constant,  has  the  value  8.316 
when  expressed  in  watt-seconds  and  F  represents  96,500  coul- 
ombs. P,  however,  is  a  specific  property  of  the  metal  in  question 
and  does  not  vary.  If  the  value  of  p  is  kept  the  same  for  a  series 
of  metals  of  the  same  valence  n,  it  is  obvious  that  the  observed 
values  of  E  will  be  proportional  to  the  values  of  P  for  the  different 
metals.  The  tendency  of  one  metal  to  precipitate  another 
depends  upon  the  values  of  E  under  the  conditions  in  question, 
and  it  is  often  true  that  with  metals  A  and  B  the  value  of  EA 
is  greater  than  EB  when  PB  is  larger  than  PA  and  this  is  why  a 
metal  will  not  always  precipitate  another  metal  that  follows  it  in 
electrochemical  series;  it  will  do  so  if  the  values  for  p  are  equal. 

To  precipitate  a  metal  at  the  cathode  by  means  of  the  electric 
current,  it  is  necessary  to  overcome  the  electromotive  force  E, 
or  oxidation  potential,  and  the  so-called  decomposition-potential 
is  reached  as  soon  as  the  value  of  E  is  exceeded.  It  follows 
from  the  Nernst  formula  that  the  decomposition  voltages  in- 
crease as  the  solution  becomes  more  dilute  and  this  is  a  well- 
known  fact. 

If  we  substitute  the  values  for  F  and  R  in  the  formula,  assume 
that  the  measurements  are  made  at  a  laboratory  temperature  of 


ELECTROMETRIC  METHODS  269 

18°C.  and  divide  by  0.4343  to  change  natural  logarithms  to 
common  logarithms,  equation  (2)  becomes 

0.058  .      P 

*.-  rjr  iogp  0) 

If  the  following  metals  are  placed  in  normal  solutions  of  their 
soluble  and  highly  ionized  salts  and  the  resulting  potential 
differences  measured  against  a  normal  hydrogen  electrode  as 
arbitrary  zero,  the  values  will  be  approximately:  K  =  2.93, 
Na  =  2.72,  Ba  =  2.8,  Ca  =  2.6,  Mg  =  1.5,  Mn  =  1.08, 
Zn  =  0.77,  Fe  =  0.43,  Pb  =  0.12,  H  =  +0.0,  Cu  =  -0.34, 
Ag  =  -0.8,  Hg  =  -0.86,  Au  =  -1.5. 

The  positive  charge  in  this  table  signifies  that  the  current 
flows  in  the  solution  from  the  metal  to  the  hydrogen  electrode 
and  on  the  wire  from  the  hydrogen  electrode  to  the  metal  back 
to  the  starting  point;  the  metal  itself  is  negative  to  the  solution 
and,  for  this  reason,  many  authorities  substitute  —  signs  where- 
ever  +  signs  are  used  in  the  above  table  and  +  signs  for  the  — 
signs.  It  will  be  noticed  that  the  magnitude  of  the  observed 
values  does  not  follow  exactly  the  same  order  as  that  of  the 
electrochemical  series  and  this  is  due  to  the  fact  that  the  osmotic 
pressure  of  the  ions  in  a  normal  solution  of  a  bivalent  metal  is 
only  about  half  as  large  as  that  of  a  normal  solution  of  a  univalent 
metal.  Thus  the  values  for  barium  and  calcium  are  near  that  of 
sodium,  whereas  if  solutions  were  used  containing  molal  con- 
centrations of  the  ions,  the  values  for  barium  and  calcium 
would  be  much  lower  than  that  of  sodium. 

The  Nernst  formula  as  expressed  in  equation  (3)  shows  that 
when  a  metal  is  in  contact  with  its  ions,  the  observed  values  of 
E  will  fall  0.058  volt  for  each  tenfold  increase  in  the  osmotic 
pressure  of  the  ions  of  a  univalent  metal,  0.029  volt  for  each 
tenfold  increase  in  the  osmotic  pressure  of  the  ions  of  a  bivalent 
metal  and  0.019  volt  for  a  corresponding  increase  in  concentration 
of  trivalent  metal  ions.  In  the  Daniell  cell,  the  electromotive 
force  will  be  1.11  volts  if  the  copper  sulfate  and  zinc  sulfate  are 
each  of  normal  concentration.  As  the  cell  is  used  the  concentra- 
tion of  the  zinc  ions  increases  and  that  of  copper  ions  diminishes, 
but  the  concentration  of  the  latter  would  have  to  be  about 
10~37  normal  before  there  would  be  as  much  tendency  for  copper 
to  dissolve  as  for  zinc. 


270  CHEMICAL  ANALYSIS  OF  METALS 

A  galvanic  cell  similar  to  the  Daniell  cell  can  be  made  with 
many  other  pairs  of  metals  and  the  farther  apart  the  elements  are 
in  the  electrochemical  series,  the  greater  will  be  the  voltage  of 
the  cell.  Since  the  potential  of  a  metal  against  a  solution  varies 
with  the  concentration  of  the  latter  it  is  evident  that  silver 
immersed  in  0.1 -normal  silver  nitrate  solution  will  have  less 
tendency  to  dissolve  than  silver  immersed  in  0.01 -normal  silver 
nitrate  solution.  A  so-called  concentration  cell  may  be  con- 
structed in  which  the  positive  to  negative  direction  may  be 
represented  as  follows: 

on  the  wire 


0.01-normal  Ag+  //0.1-normal  Ag+  /Ag 


in  the  cell 

The  actual  voltage  of  such  a  cell  has  been  found  to  be  0.055  volt 
which  is  near  the  theoretical  value  0.058  which  the  Nernst  rule 
indicates  would  be  found  if  the  0.1  -normal  solution  yielded 
exactly  ten  times  as  many  ions  as  the  0.01-normal  solution  and 
if  there  were  no  differences  in  potential  at  any  other  part  of  the 
circuit. 

The  Nernst  formula  applied  to  concentration  cells  is 

0.058  .      Cl 

E18=    —    log-  (4) 

in  which  E  and  n  have  the  usual  meaning  and  Ci  and  c2  represent 
the  concentration  of  the  ions  at  the  two  electrodes. 

The  Daniell  cell  depends  upon  the  oxidation  of  zinc  and  the 
reduction  of  copper.  A  cell  can  be  constructed  from  substances 
involved  in  any  reaction  of  oxidation  and  reduction.  Thus 
a  cell  can  be  constructed  on  the  basis  of  the  reduction  of  ferric 
ions  by  means  of  hydrogen  sulfide  and  the  reaction  will  take 
place  without  any  of  the  hydrogen  sulfide  coming  in  contact 
with  any  of  the  ferric  salt  if  suitable  electrical  contact  is  provided. 
To  make  such  a  cell,  place  a  platinum  electrode  in  a  beaker 
containing  ferric  chloride  solution  and  c'onnect  this  electrode  by 
means  of  a  wire  with  another  platinum  electrode  immersed  in 
sodium  chloride  solution.  Connect  the  two  solutions  also  by 


ELECTROMETRIC  METHODS  271 

means  of  a  salt  bridge;  this  may  take  the  form  of  an  inverted 
U-tube  filled  with  salt  solution.  Now  pour  hydrogen  sulfide 
water  into  the  beaker  containing  the  sodium  chloride  solution. 
The  hydrogen  sulfide  will  be  reduced  to  sulfur  and  hydrogen  ions 
will  be  formed  in  one  beaker;  the  ferric  ions  will  be  reduced  to 
ferrous  ions  in  the  other  beaker  and  the  direction  of  the  current  is 
indicated  by  the  following  diagram: 

on  the  wire 


Pt/H2S  /NaCl/Fe+  +  + 
III  I 


in  the  cell 

Some  of  the  most  important  electrometric  methods  are  based 
upon  potential  measurements  which  indicate  the  concentration 
of  hydrogen  ion  in  a  solution. 

Water  ionizes  slightly  into  hydrogen  and  hydroxyl  ions: 

H2O  ->  H+  +  OH-  (5) 

The  mass  action  law  applied  to  this  ionization  reaction  is 

(cone.  H+)  X  (cone.  OH") 

—7 —     — TT  c\\  -  =  a  constant, 

(cone.  H2O) 

In  a  sample  of  pure  water  at  18°,  the  concentration  of  the 
hydrogen  ion  expressed  in  moles  per  liter  is  about  10~7  and  in 
these  units  the  concentration  of  the  hydroxyl  ion  is  the  same. 

Now  in  reaction  (5)  the  concentration  of  the  water  is  not 
changed  appreciably  by  any  changes  of  ionization  that  may  take 
place  in  dilute  solution,  so  that  from  equation  (5)  we  may  say 
(cone.  H+)  X  (cone.  OH")  =  lO"14  for  any  solution  at  18°. 
If  a  hydrogen  electrode  is  placed  in  a  solution  together  with  a 
standard  electrode  of  known  electromotive  force,  the  measure- 
ment of  the  difference  in  potential  between  the  two  electrodes 
will  indicate  the  concentration  of  the  hydrogen  ions  in  the  solution. 
Besides  determining  the  actual  hydrogen  ion  concentration, 
the  neutralization  of  an  acid  by  a  base  can  be  followed  even  in 
solutions  which  are  highly  colored  and  the  exact  neutral  point 
can  be  determined  in  many  cases  more  accurately  than  it  is 
possible  to  titrate  by  means  of  the  usual  indicators  in  a  perfectly 
clear  solution. 


272 


CHEMICAL  ANALYSIS  OF  METALS 


The  potential  of  the  normal  hydrogen  electrode  is  0.28  volt 
below  the  absolute  zero  potential  at  25°.  That  of  the  calomel 
electrode  is  -0.28  volt  referred  to  a  normal  hydrogen  electrode 
or  -0.56  volt  on  the  absolute  scale  at  25°C.  when  normal  KC1  is 
used  as  electrolyte. 

Hildebrand1  used  an  apparatus  for  electrometric  titration 
which  is  illustrated  by  the  diagram  shown  in  Fig.  32.2  The 
beaker  in  which  the  titration  is  made  contains  the  hydrogen 

electrode,  h,  and  the  calomel 
electrode,  C.  The  former 
consists  of  an  S-shaped  plati- 
num electrode  covered  with 
platinum  black  and  kept  sat- 
urated with  hydrogen  gas, 
H2,  introduced  through  the 
side  arm  of  an  enveloping 
tube.  The  calomel  electrode 
is  connected  through  the 
switch  K  with  the  galvano- 
meter G  and  thence  to  the 
positive  pole  of  the  battery 
B.  By  means  of  the  sliding 
contact  S  a  variable  frac- 
tion of  the  current  from  the  battery  passes  through  the  gal- 
vanometer to  the  calomel  electrode  opposing  the  current  which 
arises  from  the  difference  in  potential  between  the  electrodes 
dipping  in  the  titrated  solution.  By  pressing  the  key,  K,  and 
moving  the  sliding  contact  until  the  galvanometer  needle  shows 
no  current,  the  voltmeter  V  gives  the  potential  of  the  current 
which  corresponds  exactly  to  that  between  the  two  electrodes. 
This  method  gives  an  accuracy  of  1  or  2  per  cent  in  the 
determination  of  the  electromotive  force  and  this  gives  satis- 
factory results  in  many  titrations.  An  accuracy  of  about  0.03 
per  cent  in  the  voltage  measurement  can  be  obtained  by  using 
a  potentiometer,  such  as  type  K  of  the  Leeds  and  Northrup 
Company. 

In  oxidimetric  titrations,  which  are  of  special  interest  in  the 

i /.  Am.  Chem.  Soc.,  35,  847  (1913). 

2  Reproduced  by  permission  from  the  catalog  of  A.  H.  Thomas  Co. 


FIG.  32. 


ELECTROMETRIC  METHODS 


273 


analysis  of  iron  and  steel,  the  method  of  procedure  is  similar 
except  that  a  polished  platinum  electrode,  exposing  as  little 
surface  as  possible  to  the  solution,  is  substituted  for  the  hydrogen 
electrode  and  the  calomel  electrode  is  connected  to  the  negative 
pole  of  the  battery  B.  Palladium  is  unsuitable  as  an  electrode, 
probably  because  of  its  tendency  to  occlude  hydrogen,  and  pure 
gold  is  better  than  an  alloy  of  gold  and  palladium,  but  even  gold 
is  inferior  to  polished  platinum.  Poor  results  are  likely  to  be 
obtained  with  a  dirty  electrode.  An  electrode  should  be  cleaned 
before  using  it  by  treatment  with  acid  followed  by  ge'ntle  ignition 
and  should  be  kept  under  hydrochloric  acid  between  titrations. 


H  +  Concentrations 

5,  5,  o,  o,  o,  o  S,  5,  o,  5  5,  o,  5,  o, 

oSc!;Si=:S<ia>-j<i><ji^.Jgnj-!- 

\ 

\ 

\ 

\ 

^ 

* 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

^ 

s 

\ 

\ 

\ 

}      0.4        0.5       0.6       0.7        0.8       0.9        1.0       I.I 
E  M  F  (Vo!H) 

FIG.  33. 

For  the  most  accurate  results  in  electrometric  titrations, 
whether  acidimetric  or  oxidimetric,  the  titrated  solution  should 
be  stirred  mechanically  and  the  potentials  observed  during  the 
titration  should  be  plotted  against  the  volumes  of  standard 
solution  added.  For  most  oxidimetric  titrations,  however,  it  is 
not  at  all  necessary  to  know  the  exact  value  of  the  potential. 
During  the  progress  of  the  titration,  a  slow  change  in  voltage  takes 
place  but  at  the  end-point  there  is  almost  always  a  sudden  change. 

Figure  33  shows  the  relation  between  measured  potential 
differences  of  a  hydrogen  electrode  in  solutions  of  varying  de- 
grees of  acidity  compared  with  the  normal  hydrogen  electrode. 
If  the  concentration  of  H+  is  designated  as  c,  formula  (4)  on 
p.  270  becomes 

EIS    =  0.058  log- 
c 

18 


274 


CHEMICAL  ANALYSIS  OF  METALS 


To   compute   the  actual  H   concentration   from   the   observed 

voltage  the  value  of  log  -  is  obtained  first  and  Sorensen  has 

c 

suggested  that  this  value  be  called  the  pH  of  the  solution  in 
question,  or  the  hydrogen  ion  exponent.  In  Fig.  33  the  values 
given  on  the  left  represent  the  actual  concentration  of  H+  and 
the  values  on  the  right  are  those  of  pH. 

Figure  34  shows  independent  curves  obtained  by  Hildebrand 


0.9 


0.8  — 


— "Neutral  Point1 


icr- 


IO-2 


FIG.  34. 

in  the  titration  of  acetic  and  hydrochloric  acids  using  a  hydrogen 
electrode  against  a  calomel  electrode.  At  the  neutral  point,  the 
concentration  of  H+  is  10~7  as  in  pure  water.  In  the  case  of 
acetic  acid,  the  curve  shows  that  it  is  a  weak  acid  and  that  normal 
sodium  acetate  is  easily  hydrolyzed  and  gives  an  alkaline  reaction. 
Soon  after  the  publication  of  Hildebrand's  paper,  Forbes  and 
Bartlett1  published  a  method  of  titrating  ferrous  salts  by  dichro- 

1  J.  Am.  Chem.  Soc.,  35,  1527  (1913).     Crotagno  in  1900  had  proposed 
using  electrometric  titrations  for  oxidimetric  methods  of  analysis. 


ELECTROMETRIC  METHODS 


275 


mate  with  a  somewhat  simpler  apparatus.  Instead  of  the 
voltmeter  and  rheostat,  a  thin  wire  of  manganin,  German  silver 
or  nichrome  was  stretched  over  a  strip  of  wood  and  provided 
with  a  sliding  contact.  During  the  progress  of  the  reaction,  the 
sliding  contact  was  moved  so  that  the  galvanometer  needle 
showed  little  if  any  deflection  but  on  reaching  the  end-point,  one 
drop  of  dichromate  sent  the  galvanometer  needle  off  the  scale. 
Roberts  and  Hostetter1  have  shown  how  a  few  tenths  of  a 


370 
350 
330 
310 
Z90 


1*0 


210 


190' 


no 


150 


4         5          6         7         8         9         10        II 
cc.I 

FIG.  35. 


milligram  of  tin,  chromium,  ferrous  or  ferric  iron  can  be  deter- 
mined with  accuracy  by  a  simple  electrometric  titration,  and 
Roberts2  has  shown  how  a  sensitive  potentiometer  can  be  made 
at  a  relatively  low  cost. 

Figure  35  shows  results  obtained  by  Robinson  and  Winter3 
in  the  electrometric  titration  of  the  arsenite  in  a  sample  of 
London  purple  with  tenth-normal  iodine. 

1  J.  Am.  Chem.  Soc.,  41,  1337  (1919). 

2 /tod.,  41,  1358  (1919). 

3J.  Ind.  Eng.  Chem.,  12,  775  (1920). 


276 


CHEMICAL  ANALYSIS  OF  METALS 


Figure  36  shows  results  obtained  by  Roberts  and  Hostetter 
in  titrating  iron.  These  curves  are  selected  at  random  merely  to 
give  an  idea  of  the  sudden  change  in  oxidation  potential  that 
takes  place  at  the  end-point  of  the  reaction. 

Several  electrometric  methods  which  have  been  found  success- 
ful in  busy  testing  laboratories  have  been  proposed  by  G.  L. 
Kelley1  and  his  co-workers  of  the  Mid  vale  Steel  Company  and 
they  have  devised,  with  the  aid  of  Leeds  and  Northrup,  a  special 
apparatus  for  these  electrometric  titrations.  Two  views  of  this 
apparatus2  are  shown  in  Figs.  37  and  38. 


(00 

600 
500 

j>400 
.1  300 

+100 
0 

-100 

( 

/ 

/ 

} 

1-    

•         i 



>'        —<j 

1  —  - 

>-a—  o- 

^•^(XT- 

^^ 

1 

I         3         4         567         8        9        10        II        \Z        13        14        15 
cc.O.OIN  KzCr£0-j 

FIG.  36. 

The  apparatus  consists  essentially  of  a  wooden  case  with  an 
upright  carrying  the  motor,  burettes  and  electrodes.  In  the  case 
are  two  dry  cells,  an  adjustable  resistance,  and  a  reflecting  gal- 
vanometer. On  the  upper  surface  of  the  case  is  a  ground  glass 
scale  on  which  the  light  from  the  galvanometer  is  thrown.  A 
knurled  head  inside  of  the  case  permits  of  adjusting  the  zero 
point  of  the  galvanometer  and  another  on  the  side  controls  the 
resistance. 

The  standard  carries  the  burettes,  the  electrodes,  and  the 
motor  for  driving  the  stirrer.  In  addition,  provision  has  been 

1  /.  Ind,  Eng.  Chem.,  9,  780  (1917).     Other  references  are  given  at  the 
end  of  this  chapter. 

2  These  illustrations  are  reproduced  from  the  catalog  of  A.  H.  Thomas 
Co.  (1920). 


ELECTROMETRIC  METHODS 


277 


made  for  a  reservoir  of  the  electrolyte  which  is  used  in  the  calomel 
cell.  This  makes  possible,  without  change  in  its  potential,  the 
displacement  of  the  impure  electrolyte  which  may  have  accumu- 
lated in  the  tip  of  the  electrode.  A  pan  on  an  adjustable  support, 
specially  treated  to  resist  acids,  carries  the  beaker  in  which  the 


FIG.  37. 


FIG.  38. 


titration  is  made.  Two  switches  are  mounted  on  the  sides  of  the 
case,  one  of  which  controls  the  galvanometer  light  and  motor, 
while  the  other  closes  the  potentiometer  circuit. 

To  operate  the  instrument,  a  beaker  containing  the  solution  to 
be  analyzed  is  placed  on  the  pan  and  the  support  raised  and 
locked  in  position.  The  switch  controlling  the  galvanometer 


278  CHEMICAL  ANALYSIS  OF  METALS 

light  and  motor  is  then  closed.  The  other  switch  closes  the 
potentiometer  circuit  and  a  slight  turn  of  the  knob  controlling  the 
resistance  is  sufficient  to  bring  the  beam  of  light  on  the  scale.  In 
titrating  a  series  of  solutions,  this  latter  adjustment  need  be  made 
only  once.  During  the  operation,  which  is  quick,  certain  and 
convenient,  the  analyst  watches  the  beam  of  light  until  a  perma- 
nent change  of  potential  is  noted.  In  general,  the  first  permanent 
large  change  marks  the  end-point  of  the  reaction. 

A  rheostat  for  varying  the  speed  of  the  motor  stirrer  is  mounted 
on  a  casting  attached  to  the  box. 

DESCRIPTION  OF  COMPONENTS 

Calomel  Electrode  Cell  (Fig.  39). — The  calomel  electrode  rests  in  a  metal 
collar  attached  to  the  upright  at  E.  The  glass  stopcock  at  B  allows  liquid  to 
flow  into  the  cell  from  the  reservoir  to  which  it  is  connected  by  rubber 
tubing  at  A.  When  this  stopcock  is  opened,  the  capillary  tube  at  D  is 
flushed,  thus  insuring  the  purity  of  the  electrolyte  in  the  cell.  The  cell 
may  be  filled  through  the  opening  at  (7,  which  is  then 
closed.  A  platinum-tipped  wire  at  F  makes  contact  with 
the  external  circuit.  The  capacity  of  the  cell  is  about 
100  c.c.  A  small  amount  of  mercury  is  placed  in  the 
bottom  of  the  cell  and  covered  with  Hg2Cl2.  The  cell  is 
then  filled  with  the  neutral  liquid,  a  normal  solution  of 
KC1.  This  gives  a  constant  potential  difference  of  about 
0.56  volt  between  the  Hg  and  the  solution,  the  Hg  being 
+  to  the  solution. 

Potentiometer. — The  e.m.f.  of  the  electrolytic  cell  is 
balanced  against  the  fall  of  potential  across  a  slide  wire 
in  circuit  with  two  dry  cells  and  a  resistance.     The  total 
resistance  of  the  slide  wire  is  about  50  ohms.     This  resist- 
FIG.  39.  ance  can  be  varied,  to  secure  a  balance,  by  means  of  a 

knurled  head  on  the  outside  of  the  case. 

Galvanometer. — A  Leeds  and  Northrup  Company  Reflecting  Galvan- 
ometer is  used  with  this  outfit.  This  instrument  is  sufficiently  sensitive  for 
the  purpose  and  has  the  further  advantage  of  a  very  short  period.  It  is 
rugged  in  construction  and  will  withstand  as  much  rough  usage  as  an  ordi- 
nary voltmeter.  The  image  of  the  lamp  filament  is  reflected  to  a  translucent 
scale  which  is  placed  on  the  top  of  the  box.  This  places  the  scale  where  it 
can  most  easily  be  seen  by  the  operator  while  titrating.  The  lamp  furnished 
with  this  instrument  has  a  single  straight  filament  of  high  brilliancy. 

Heating  Unit. — A  heating  unit  is  mounted  on  a  socket  on  the  inside  of 
the  box  for  the  purpose  of  keeping  the  galvanometer  circuit  dry  at  all 
times  and  preventing  possible  "leakage"  due  to  moisture. 


ELECTROMETRIC  METHODS 


279 


Motor  and  Stirrer. — The  stirrer  consists  of  a  three-bladed  glass  propeller 
cemented  into  a  brass  rod  and  belted  to  a  small  electric  motor.  This  motor 
is  securely  attached  to  the  upright  and  is  equipped  with  a  rheostat  for 
variable  speeds. 

Reservoir. — The  reservoir  consists  of  an  aspirator  bottle,  500  c.c.  capac- 
ity, firmly  attached  to  the  upright. 

no  VOLT  CIRCUIT 


FIG.  40. 

Switches  and  Connections  (Fig.  40). — Two  switches  are  mounted  on  the 
box;  one  controls  the  motor  and  galvanometer  light,  and  the  other  throws 
in  the  potentiometer  circuit  (see  Fig.  41).  All  connections,  except  to  dry 
cells,  are  soldered  and  the  insulation  is  designed  to  prevent  all  possible 
"leaks."  All  metal  parts  are  treated  with  a  special  acid-resisting  varnish. 
The  measuring  circuit  is  carefully  insulated  from  the  motor  circuit. 

POTENTIOMETER    CIRCUIT 


The  numbers  in  Figs.  37  and  38  refer  to  the  following  parts  1,  beaker 
support;  2,  stirrer  propeller;  3  calomel  electrode  cell;  4,  stirrer  shaft;  5, 
reservoir  for  solution  used  in  the  calomel  cell;  6  and  7,  burettes;  8,  metal 
frame;  9,  platinum  electrode  tube;  10,  stirring  motor;  11,  flexible  cord  and 
plug;  12,  push  button  switch;  13,  upright  support;  14,  coil  spring  belt  for  fast- 
ening stirrer;  15,  potentiometer  box;  16,  galvanometer  switch;  17:  rheostat 
for  varying  speed  of  stirrer;  18,  ground  glass  scale  for  showing  position  of 
light  from  the  galvanometer  mirror. 


280  CHEMICAL  ANALYSIS  OF  METALS 

1.  ELECTROMETRIC  DETERMINATION  OF  CHROMIUM  IN  STEEL1 

Principle. — The  steel  is  dissolved  in  sulfuric  acid,  carbides  are 
decomposed  by  evaporating  and  the  ferrous  iron  is  oxidized  by 
means  of  nitric  acid.  By  ammonium  persulfate  in  the  presence 
of  silver  ions,  the  chromic  ions  are  oxidized  to  chromic  acid. 
The  excess  of  persulfate  is  destroyed  by  boiling  and  any  per- 
manganate is  reduced  by  the  careful  addition  of  hydrochloric 
acid.  The  cold  solution  is  then  titrated  with  freshly-standard- 
ized ferrous  sulfate  solution,  using  the  electrometric  apparatus 
for  determining  the  end-point. 

Cr  +  3H2SO4-*Cr2(SO4)3  +  3H2  T    (solution  in  acid) 
2Cr+++  4-  3S2O8=  +  6H20-+2OO3  +  6SO4=  +  12H+  (with 

Ag+  as  catalyzer) 
Cr03  +  3Fe++  +  6H+->Cr+++  +  3Fe+++  +  3H2O 

Solutions  Required. — 1.  Sulfuric  Acid  (d.  1.2). — Pour  con- 
centrated sulfuric  acid  into  five  times  as  much  water;  the  diluted 
acid  is  approximately  6-normal. 

2.  Silver  Nitrate  Solution. — Dissolve  2.5  g.  of  solid  in  1  liter 
of  water;  this  solution  is  approximately  0.015-normal. 

3.  Potassium  Dichromate.     Dissolve  2.83  g.  of  pure  dichromate 
crystals  and  5  g.  of  sodium  carbonate  in  enough  water  to  make 
exactly  1  liter;  this  solution  is  0.0577-normal  and  1  c.c.  =  0.001  g. 
of  chromium.     Commercial  dichromate  should  be  recrystallized 
and  dried  at  150°  for  several  hours. 

4.  Ferrous  Sulfate  Solution. — Mix  23  g.  of  pure  ferrous  ammo- 
nium sulfate  with  50  c.c.  of  concentrated  sulfuric  acid  and  dilute 
slowly  with  water.     When  cold,  dilute  to  exactly  1  liter.     This 
solution  is  0.0587-normal  when  freshly  prepared.     The  solution 
is  intentionally  made  a  little  stronger  than  the  dichromate  solu- 
tion because  it  gradually  oxidizes  on  standing  and   becomes 
weaker  as  a  reducing  agent.     In  a  busy  laboratory  it  is  often 
convenient  to  have  the  two  solutions  of  exactly  the  same  strength 
and  this  can  be  done  each  day  by  diluting  enough  of  the  ferrous 
sulfate  solution  for  the  day's  use  as  determined  by  daily  standardi- 
zation of  the  solution. 

IKELLEY  and  Others:  /.  Ind.  Eng.  Chem.,  8,  722  (1916);  9,  632,  780 
(1917). 


ELECTROMETRIC  METHODS  281 

For  steel  analysis,  it  is  safe  to  depend  upon  the  purity  of  re- 
crystallized  potassium  dichromate  provided  a  fresh  solution  is 
made  up  each  week.  The  strength  of  the  ferrous  sulfate  solution 
must  be  checked  daily.  It  can  be  titrated  against  the  dichromate 
solution  electrometrically. 

If  it  is  desired  to  check  the  value  of  the  potassium  dichromate 
solution,  a  convenient  method  is  to  titrate  the  ferrous  sulfate 
solution  against  permanganate  which  has  been  standardized 
against  sodium  oxalate  (p.  62)  and  then  titrate  the  ferrous  sul- 
fate against  dichromate  in  the  electrometric  apparatus. 

Procedure. — Dissolve  1  g.  of  the  steel  in  70  c.c.  of  sulfuric  acid 
(d.  1.2).  If,  however,  less  than  0.5  per  cent  of  chromium  is 
likely  to  be  present,  use  twice  as  much  sample  and  not  over  100 
c.c.  of  acid  and  if  more  than  5  per  cent  of  chromium  is  present, 
use  correspondingly  less  steel  without  changing  the  volume  of 
sulfuric  acid.  Samples  need  not  be  weighed  closer  than  to  the 
nearest  milligram. 

If  carbides  are  left  unattacked,  as  shown  by  a  turbidity  and 
sometimes  by  dark  particles,  evaporate  the  solution  until  salts 
begin  to  crystallize.1  Dilute  carefully  with  water  to  50  c.c., 
heat  to  boiling  and  oxidize  the  iron  by  adding  about  2  c.c.  of 
concentrated  nitric  acid,  drop  by  drop.  The  nitric  acid  is  added 
until  the  dark-brown  color  of  FeSO4.xNO  disappears.  Boil  the 
solution  about  5  min.  to  expel  oxides  of  nitrogen.  Dilute  with 
hot  water  to  a  volume  of  250  to  300  c.c.,  add  10  c.c.  of  silver 
nitrate  solution  and  20  c.c.  of  ammonium  persulfate  solution. 
Do  not  add  these  solutions  in  the  reverse  order,  as  in  the  absence 
of  silver  ions  the  oxidation  of  chromium  and  manganese  does  not 
take  place  in  the  desired  manner.  When  manganese  is  present, 
permanganic  acid  is  formed.  Boil  the  solution  vigorously  for 
10  min.  If  the  solution  contains  chlorides  which  would  interfere 
with  the  reaction,  this  is  shown  by  the  formation  of  silver  chloride 
precipitate.  If  the  oxidation  of  the  chromium  is  incomplete, 
the  red  color  of  the  permanganate  will  not  appear  from  the  man- 
ganese in  the  steel.  In  that  case  add  more  silver  nitrate  and  a 

1  If  this  method  fails  to  decompose  carbides,  dissolve  another  sample  in 
60  c.c.  of  6-normal  hydrochloric  acid,  add  nitric  acid  to  oxidize  the  iron  and 
evaporate  to  fumes  in  order  to  remove  all  hydrochloric  acid.  The  treat- 
ment to  destroy  carbides  appears  to  be  unnecessary  with  tungsten  steels. 


282  CHEMICAL  ANALYSIS  OF  METALS 

fresh  portion  of  ammonium  persulfate.  While  the  solution  is 
still  boiling  add  5  c.c.  of  3-normal  hydrochloric  acid  to  decompose 
the  permanganate  into  soluble  manganous  salt  and  boil  at  least 
5  min.  longer  to  remove  any  chlorine  formed  and  to  make  sure 
that  the  persulfate  is  all  decomposed.  Cool  to  about  20°  and 
titrate  electrometrically. 

In  titrating,  first  bring  the  beam  of  light  near  the  left  end  of 
the  scale.  Add  standard  ferrous  sulfate  slowly  until  the  beam 
of  light  has  been  moved  permanently  toward  the  right.  Then 
add  standard  potassium  dichromate  until  the  light  will  move  no 
farther  toward  the  left  and  finish  the  titration  by  adding  ferrous 
sulfate  carefully  until  a  small  permanent  displacement  is  again 
obtained. 

Computation. — If  the  concentration  of  the  potassium  dichro- 
mate and  ferrous  ammonium  sulfate  solutions  is  adjusted  so 
that  1  c.c.  of  each  is  equivalent  to  1  mg.  of  chromium,  the  per 
cent  of  chromium  in  a  sample  of  steel  weighing  1  g.  is  found  by 
subtracting  the  volume  of  potassium  dichromate  solution  used 
from  the  total  volume  of  ferrous  ammonium  sulfate  and  moving 
the  decimal  point  one  place  to  the  left. 

In  general,  if  s  represents  the  weight  of  sample,  N  the  normal- 
ity of  the  potassium  dichromate  solution  and  /  the  value  of 
1  c.c.  of  ferrous  ammonium  sulfate  in  terms  of  the  potassium 
dichromate  solution,  then,  when  a  c.c.  of  ferrous  solution  and 
b  c.c.  of  dichromate, 

(aXf-b)NX  0.01733  X  100 

-  =  per  cent  Cr 

NOTES. — In  titrating  sodium  oxalate  with  potassium  permanganate  there 
is  no  advantage  in  using  the  electrometric  apparatus  but  with  it  better  re- 
sults are  obtained  than  by  other  methods  in  titrating  (1)  permanganate  and 
ferrous  sulfate,  (2)  chromate  and  ferrous  sulate  sulfate  and  (3)  chromate  + 
excess  ferrous  sulfate  +  permanganate  +  ferrous  sulfate  to  end-point.  In 
titrating  a  chromate  solution,  the  addition  of  ferrous  ions  usually  causes  at 
first  an  anomalous  rise  but  with  permanganate  solution  this  anomaly  does 
not  appear  with  the  same  regularity  and  is  less  marked.  In  titrating  di- 
chromate with  ferrous  sulfate,  the  change  in  potential  is  always  abrupt  when 
the  end-point  is  reached  but  with  permanganate  and  ferrous  sulfate  the  end- 
point  is  not  so  sharp;  it  is  advisable,  therefore,  to  add  ferrous  sulfate  in 
excess  until  a  marked  change  in  potential  takes  place,  then  add  perman- 
ganate until  the  original  potential  is  reached  or  until  2  or  3  drops  produce  no 


ELECTROMETRIC  METHODS  283 

further  change  and  then  finish  with  ferrous  sulfate  solution.  Probably 
during  the  first  addition  of  ferrous  sulfate  to  permanganate  some  colloidal 
manganese  dioxide  is  formed  which  requires  an  excess  of  ferrous  sulfate  to 
decompose  it.  In  the  final  stage  this  manganese  dioxide  suspension  is  not 
formed  and  a  sharper  end-point  results. 

If  vanadium  is  present  it  will  be  titrated.  In  this  event  use 
the  end-point  described  in  the  vanadium  determination.  The 
chromium  may  be  calculated  as  follows :  Multiply  the  vanadium 
titration  as  found  in  a  separate  determination  of  vanadium  by 
0.339,  which  gives  the  amount  to  be  subtracted  from  the  titration 
of  chromium  and  vanadium  together. 

Tungsten  does  not  interfere  with  this  determination  if  the 
volume  of  the  solution  is  not  too  great  at  the  time  of  oxidation 
with  nitric  acid.  Tungstic  acid  does  not  occlude  chromium, 
although  it  does  occlude  vanadium.  When  chromium  and 
vanadium  are  oxidized  together  by  ammonium  persulfate  and 
silver  nitrate,  the  oxidation  of  chromium  is  complete,  and  of 
the  vanadium  only  that  part  which  is  retained  by  the  WO3 
remains  unoxidized. 

If  the  end-point  obtained  on  titrating  is  not  sharp,  25  c.c.  of 
sulfuric  acid  (d.  1.58)  may  be  added.  Results  by  this  method 
are  said  to  be  excellent,  and  remarkably  concordant  values 
are  obtained  with  low  chromium  content. 

2.  RAPID   METHOD   FOR  DETERMINING  CHROMIUM  IN   STEEL 

Principle. — The  sample  is  dissolved  in  nitric  acid  containing 
about  2.5  mgs.  of  manganese  as  sulfate.  The  nitric  acid 
solution  is .  treated  with  sodium  bismuthate  under  conditions 
such  that  the  formation  of  permanganic  acid  indicates  a  satis- 
factory oxidation  of  the  chromium,  sulfuric  acid  is  added,  and 
enough  hydrochloric  acid  to  reduce  the  permanganic  acid  without 
affecting  the  chromic  acid.  The  cold  solution  is  then  titrated 
with  the  electrometric  apparatus  as  in  Method  1. 

Solutions  Required. — Nitric  Acid  (d.  1.13)  (cf.  p.  50)  con- 
taining 0.2  g.  of  manganese  sulfate  per  liter. 

Sulfuric  Acid  (d.  1.58)  made  by  adding  concentrated  acid 
to  2.5  times  as  much  water. 

The  other  reagents  are  the  same  as  in  Method  1. 


284  CHEMICAL  ANALYSIS  OF  METALS 

Procedure. — Dissolve  1  g.  of  the  sample  by  heating  with  50  c.c. 
of  the  nitric  acid  solution  and  boil  1  min.  after  solution  is  complete. 
Add  20  c.c.  water  and  heat  just  to  boiling.  Remove  from  the 
hot  part  of  the  plate  and  add  2  g.  sodium  bismuthate.  Boil 
gently  at  least  2  min.  If  the  color  of  permanganic  acid  is  not 
pronounced  at  the  end  of  this  time,  make  a  second  addition  of 
sodium  bismuthate  and  boil  again. 

The  color  of  permanganic  acid  should  be  marked  at  the  time 
of  taking  the  next  step  in  the  determination.  This  consists  in 
adding  enough  boiling  water  to  make  200  c.c.,  40  c.c.  of  dilute 
sulfuric  acid  and  15  c.c.  of  dilute  hydrochloric  acid.  Boil 
2  min.  after  the  color  of  permanganic  acid  disappears.  Then  add 
finely  crushed  ice  and  titrate  electrometrically. 

NOTES  AND  PRECAUTIONS. — The  method  is  applicable  to  steels 
containing  2.5  per  cent  of  chromium  and  which  have  not  been 
forged  or  subjected  to  complete  heat  treatment.  In  the  latter 
case  carbides  cause  low  results.  Heating  a  cast  piece  above  the 
critical  temperature,  quenching  and  drawing  do  not  prevent 
analysis  by  this  method. 

If  vanadium  is  present  this  will  be  oxidized  and  titrated  with 
chromium. 

Manganese  is  added  to  the  nitric  acid  to  insure  the  presence 
of  0.3  to  0.6  per  cent  of  manganese  in  the  sample  to  -be  analyzed. 
The  manganese,  through  the  formation  of  permanganic  acid,  is 
a  convenient  indicator  of  the  success  of  the  oxidation.  If  present 
in  amounts  greater  than  0.75  per  cent,  Mn02  is  precipitated 
in  a  form  which  resists  solution  by  dilute  hydrochloric  acid.  It 
is  possible  that  the  permanganic  acid  assists  in  the  decomposition 
of  carbides. 

The  20  c.c.  of  water  is  added  to  facilitate  the  oxidation  of  the 
manganese  to  permanganic  acid.  If  the  water  is  added  in  a  more 
dilute  nitric  acid,  the  dissolving  of  the  sample  is  delayed  and 
carbides  are  not  attacked.  If  the  amount  of  water  is  greater, 
the  bismuthate  and  permanganic  acid  do  not  decompose  the 
chromium  carbides.  If  the  amount  of  water  is  less,  more  man- 
ganese dioxide  is  formed  and  there  is  an  incomplete  oxidation 
of  the  chromium  present  as  carbide. 

When  the  amount  of  chromium  carbide  is  small,  one  addition 
of  sodium  bismuthate  will  be  sufficient.  An  index  of  the 


ELECTROMETRIC  METHODS  285 

presence  of  sufficient  bismuthate  is  the  persistence  of  the  color 
of  permanganic  acid  during  2  min.  of  gentle  boiling.  When  it 
does  not  persist,  a  second  addition  must  be  made.  Gentle 
boiling  prevents  a  too  great  change  in  concentration  by  evapo- 
ration. In  the  case  of  samples  taken  from  preliminary  tests 
a  second  addition  will  generally  not  be  necessary,  but  no  rule 
as  to  this  can  be  laid  down. 

When  oxidation  is  complete  and  water  is  added,  a  precipitate 
of  bismuth  subnitrate  appears.  This  dissolves  upon  the  addition 
of  sulfuric  acid.  At  this  point  the  color  of  the  solution  should 
indicate  an  appreciable  quantity  of  undecomposed  permanganic 
acid.  Turbidity  may  be  due  to  carbides  or  manganese  dioxide. 
Carbides  will  not  be  present  when  the  method  is  properly  applied 
to  the  classes  of  steel  for  which  it  has  been  found  suitable. 
Manganese  dioxide  will  be  formed  only  in  small  amounts  under 
the  conditions  described,  when  the  total  amount  of  Mn  present 
does  not  exceed  0.75  per  cent.  Such  amounts  as  do  form  may 
be  readily  decomposed  along  with  the  permanganic  acid  by 
boiling  two  minutes  after  the  addition  of  hydrochloric  acid. 

The  sulfuric  acid  prevents  the  precipitation  of  bismuth 
oxychloride  during  boiling  to  decompose  manganese  compounds. 

The  finished  solution  should  have  a  bright  yellow  or  orange 
color,  and  turbidity  or  undissolved  material  should  be  due  only 
to  the  presence  of  a  precipitate  of  bismuth  oxychloride. 

3.  DETERMINATION     OF    MANGANESE    BY    THE    BISMUTHATE 

METHOD1 

Principle. — Manganous  nitrate  formed  by  dissolving  the  steel 
in  nitric  acid,  is  oxidized  by  sodium  bismuthate  in  the  usual  way 
and  the  permanganic  acid  is  titrated  with  standard  mercurous 
nitrate  solution.  With  this  reducing  agent  the  permanganic 
acid  appears  to  be  reduced  according  to  the  following  equation : 

4  MnO4~  +  7Hg2++  +  20H+-+3MnO2  +  Mn++  +  14Hg++  + 

10H2O 

or  4Mn04~  +  7Hg2++  +  32H+-»3Mn++++  +  Mn++  +  14Hg++ 

+  16H2O 

1  KELLY  and  Others,  J.  I.  E.  C.,  10,  19  (1918). 


286  CHEMICAL  ANALYSIS  OF  METALS 

The  manganese  dioxide  is  not  precipitated  at  the  prescribed 
acidity  and  at  a  low  temperature;  it  exists  either  in  colloidal 
solution  or  as  a  sulfate  of  quadrivalent  manganese. 

Solutions  Required. — The  nitric  acid  and  potassium  per- 
manganate solutions  are  the  same  as  described  in  Chapter  III, 
Method  1,  but  it  is  convenient  to  adjust  the  perman- 
ganate so  that  1  c.c.  =  0.0005  g.  of  manganese.  The  sulfuric 
acid  is  as  in  Method  2  above.  The  mercurous  nitrate  is  prepared 
by  dissolving  10.5  g.  of  mercurous  nitrate  in  150  c.c.  of  water  and 
2  c.c.  of  nitric  acid;  any  un dissolved  salt  is  removed  by  decanta- 
tion  and  the  solution  made  up  to  1  liter.  Standardize  the 
solution  against  standard  potassium  permanganate  solution  in 
the  electrometric  apparatus,  or  by  precipitating  with  dilute 
sodium  chloride  in  the  presence  of  a  little  sodium  acetate  and 
filtering  off  the  mercurous  chloride  precipitate  into  a  weighed 
Gooch  crucible.  This  precipitate  may  be  dried  at  150°. 

Procedure. — Dissolve  the  steel  in  nitric  acid  and  proceed 
exactly  as  described  on  page  52  until  the  excess  of  sodium 
bismuthate  has  been  removed  by  filtration.  Add  a  little  ice 
and  50  c.c.  of  sulfuric  acid  (d.  1.58).  At  a  volume  of  250  c.c. 
and  at  a  temperature  below  40°,  titrate  in  the  electrometric 
apparatus  with  mercurous  nitrate  solution,  as  follows 

Adjust  the  resistance  to  bring  the  beam  of  light  from  the  poten- 
tiometer on  the  ground  glass  scale  and  then  add  the  standard 
mercurous  nitrate  solution.  The  beam  remains  stationary,  or 
shows  a  slight  anomalous  rise,  until  the  end-point  is  approached. 
Thereupon  the  addition  of  mercurous  nitrate  causes  the  beam  to 
move  in  the  opposite  direction  from  which  it  returns  more  or  less 
slowly  as  the  solution  is  stirred,  until  finally  it  remains  off  the 
scale  altogether.  The  addition  of  a  few  drops  of  standard 
potassium  permanganate  solution  causes  it  to  return  and  the 
titration  is  finished  by  adding  mercurous  nitrate  solution,  drop 
by  drop.  The  end-point  is  sharp,  is  not  affected  by  chromates  or 
vanadates  but  is  influenced  by  rise  of  temperature,  considerably 
more  mercurous  nitrate  being  required  if  the  titration  takes  place 
at  80°  than  at  40°. 

Computation. — If  s  represents  the  weight  of  sample  taken,  a  the 
volume  of  mercurous  nitrate  solution  used,  of  which  1  c.c.  = 
/  c.c.  of  standard  permanganate,  and  b  represents  the  volume  of 


ELECTROMETRIC  METHODS  287 

permanganate  solution  used,  of  which  1  c.c.  =  p  gm.  of  man- 
ganese, then 

(a  X  f  -  b)  p  X  100 

=  per  cent  Mn 

o 

Or,  if  the  mercurous  solution  was  standardized  gravimetrically 
and  1  c.c.  has  been  found  to  yield  q.  g.  of  Hg2Cl2  and  the 
permanganate  used  is  Abnormal,  then  when  a  c.c.  of  mercu- 
rous nitrate  and  b  c.c.  of  permanganate  were  used  with  s  g.  of 
steel, 

4MnXaX9-6XNX  0.011 
7Hg,  Cl.  X  s  - 

.0665  a  -  1.1  bN  ,  ,, 

or  -  =  per  cent  Mn 


4.  DETERMINATION     OF     MANGANESE     BY     THE     PERSULFATE 

METHOD1 

This  method  is  precisely  the  same  in  principle  as  the  foregoing 
except  that  the  manganese  is  converted  to  permanganate  by 
means  of  ammonium  persulfate  in  the  presence  of  silver  ions 
(cf.  Method  1,  p.  280)  and  is  not  reduced  by  adding  hydro- 
chloric acid.  This  method  requires  no  nitration,  as  the  excess 
of  persulfate  is  decomposed  partly  by  boiling  and  the  excess 
causes  a  constant  error.  Moreover,  although  chromium  is  oxi- 
dized to  chromate  it  does  not  interfere  when  mercurous  nitrate 
is  used  and  the  end-point  is  determined  electrometrically. 

Procedure. — Dissolve  0.5  g.  of  steel  (or  1  g.  if  the  manganese 
content  is  below  0.5  per  cent)  in  65  c.c.  of  6-normal  sulfuric  acid 
and  oxidize  the  iron  to  the  ferric  condition  by  adding  concen- 
trated nitric  acid,  drop  by  drop,  to  the  hot  solution.  After  boiling 
2  min.,  dilute  to  200  c.c.  with  hot  water,  heat  to  boiling  and  add 
10  c.c.  of  silver  nitrate  solution  and  20  c.c.  of  ammonium  per- 
sulfate as  in  Method  1.  Boil  1  min.,  cool,  add  a  little  more 
sulfuric  acid  (about  60  c.c.)  and  titrate  at  20°  with  mercurous 
nitrate  solution  as  in  Method  3. 

Computation. — It  is  convenient  to  adjust  the  concentrations 
of  the  mercurous  nitrate  and  potassium  permanganate  so  that 
1  c.c.  of  either  is  equivalent  to  0.0005  g.  of  manganese.  In  the 
case  of  the  permanganate,  39.33  c.c.  will  then  be  equivalent  to 
0.1200  g.  of  sodium  oxalate.  In  this  method  the  persulfate  is  not 

1  KELLY  and  Others,  loc.  cit. 


288  CHEMICAL  ANALYSIS  OF  METALS 

decomposed  completely  for  fear  that  some  of  the  permanganate 
will  be  reduced  as  well.  This  persulfate  causes  a  slight  difference 
in  the  ratio  between  the  permanganate  and  mercurous  standard 
solutions  but  the  effect  does  not  vary  appreciably  with  the  small 
quantities  of  persulfate  that  are  likely  to  be  present.  The  ratio 
between  the  permanganate  and  mercurous  nitrate  solutions, 
therefore,  should  be  established  electrometrically  and  a  little 
persulfate  should  be  present.  The  computation  requires  no 
explanation  if  the  solutions  are  equivalent  and  both  equal  to 
0.0005  g.  of  manganese.  A  person  without  previous  chemical 
training  can  learn  to  make  one  of  these  analyses  after  a  few  min- 
utes of  instruction. 

6.  DETERMINATION  OF  VANADIUM1 

Principle. — By  means  of  nitric  acid  of  suitable  concentration 
it  is  possible  to  oxidize  99  per  cent  of  the  vanadium  to  vanadic 
acid  without  oxidizing  any  chromium  that  may  be  present.  The 
method  is  not  quite  as  accurate  as  the  other  electrometric  methods 
which  have  been  described  and  empirical  factors  have  to  be 
assumed  to  allow  for  incompleteness  of  the  oxidation  and  for 
the  absorption  of  vanadium  by  tungstic  acid,  but  the  results  are 
seldom  more  than  0.02  per  cent  in  error  when  2  per  cent  of  vana- 
dium is  present.  By  means  of  standard  ferrous  ammonium 
sulfate  solution,  the  vanadic  acid  is  reduced  to  quadrivalent 
vanadyl  salt  and  after  adding  a  slight  excess  the  endpoint  is 
obtained  by  back  titrations  with  a  little  potassium  dichromate 
solution  and  a  few  drops  of  ferrous  sulfate  solution. 

V  +H2SO4  +  H2O-+VOSO4  +  2H2 

3VOSO4  +  HNO3  +  4H2O  ->  3HVO3  +  3H2SO4  +  2NO 
2HV03  +  2FeSO4  +  3H2SO4  ->  2VOSO4  +  Fe2(SO4)3  +  4H20 

Solutions  required. — Potassium  Dichromate. — Dissolve  0.9609 
g.  of  recrystallized  potassium  dichromate  in  distilled  water  and 
dilute  the  solution  to  exactly  1  liter  in  a  calibrated  flask.  One 
cubic  centimeter  of  this  solution  corresponds  to  0.0010  g.  of 
vanadium. 

Ferrous  Ammonium  Sulfate. — Dissolve  8  g.  of  the  salt  and  50 
c.c.  of  concentrated  sulfuric  acid  in  enough  water  to  make  1  liter. 

1  KELLY  and  Others,  J.  7.  E.  C.,  11,  632  (1919). 


ELECTROMETRIC  METHODS  289 

Adjust  this  solution  daily  so  that  it  is  equal  in  strength  to  the 
dichromate  solution.  The  strength  of  the  dichromate  solution 
should  be  verified  weekly. 

Procedure. — If  less  than  0.5  per  cent  of  vanadium  is  present, 
dissolve  2  g.  of  the  steel  in  100  c.c.  of  6-normal  sulfuric  acid; 
with  higher  percentages  of  vanadium  use  half  as  large  a  sample 
and  80  c.c.  of  sulfuric  acid.  When  the  steel  is  all  dissolved, 
oxidize  the  iron  to  the  ferric  state  by  adding  2  c.c.  of  concen- 
trated nitric  acid  to  the  hot  solution.  Boil  until  the  oxides  of 
nitrogen  are  removed  and  until  the  tungstic  acid  is  yellow,  if 
any  is  present.  Dilute  with  hot  water  to  aboufc  100  c.c.  and  add 
40  c.c.  of  concentrated  nitric  acid.  Boil  this  solution  for  an 
hour  at  such  a  rate  that  the  volume  does  not  fall  below  100  c.c. 
Cool,  dilute  to  300  c.c.  with  ice  water  and  titrate  electrometrically. 

Assume  that  the  boiling  with  nitric  acid  oxidizes  99  per  cent 
of  the  total  vanadium  content  and  that  each  per  cent  of  tungsten 
present  in  the  steel  will  absorb  0.001  per  cent  of  vanadium. 
If  difficulty  is  experienced  in  getting  the  end-point,  25  c.c.  of 
12-normal  sulfuric  acid  may  be  added  at  the  time  of  titration. 
It  does  no  harm  to  boil  the  solution  more  than  an  hour  but  if  the 
volume  falls  below  100  c.c.  there  is  danger  of  some  chromium 
being  oxidized.  In  getting  the  end-point  a  slight  excess  of  fer- 
rous sulfate  should  be  added  in  the  first  place,  then  a  smaller 
excess  of  dichromate,  finishing  with  ferrous  sulfate  solution  added 
drop  by  drop.  The  first  large  movement  is  taken  as  the  end- 
point. 

6.  THE   DETERMINATION    OF   VANADIUM    AND    CHROMIUM   IN 
FERRO  VANADIUM1 

In  this  method  of  analysis,  the  alloy  is  dissolved  in  nitric  acid, 
a  little  hydrochloric  acid  is  added  to  help  remove  carbide  and 
hydrofluoric  acid  is  used  to  dissolve  silica.  After  the  removal 
of  these  acids  by  evaporating  with  sulfuric  acid,  the  solution 
is  diluted  to  a  definite  volume  and  aliquot  parts  taken  for  further 
analysis.  In  one  portion  the  chromium  and  vanadium  are 
determined  together  as  in  Method  1  and  in  another  portion  the 
vanadium  alone  is  determined  as  in  Method  5.  The  computation 

1  Method  of  G.  L.  Kelley.  Taken  from  the  catalogue  of  F.  H.  Thomas 
Co.,  prior  to  its  publications  elsewhere  (September^  1920). 

19 


290  CHEMICAL  ANALYSIS  OF  METALS 

will  be  explained  on  the  assumption  that  standard  solutions  are 
used,  each  of  which  is  equivalent  to  1  mg.  of  chromium  per 
cubic  centimeter. 

Procedure. — Dissolve  3  g.  of  the  sample  in  75  c.c.  of  nitric 
acid  (d.  1.13).  When  solution  is  almost  complete,  add  10  c.c. 
of  HC1  to  assist  in  decomposing  carbides.  After  the  volume  has 
been  reduced  about  one-half,  add  a  few  drops  of  hydrofluoric 
acid  to  remove  silica.  Then  add  50  c.c.  of  sulfuric  acid  and 
evaporate  until  fumes  of  sulfuric  acid  appear,  with  the  object 
of  removing  all  hydrochloric  acid.  Dilute  in  a  standardized 
flask  with  water  to  1  liter.  With  a  standardized  pipette  remove 
two  100-c.c.  portions. 

To  100  c.c.,  add  20  c.c.  sulfuric  acid  and  water  to  make  300  c.c. 
Boil  and  add  silver  nitrate  and  ammonium  persulfate  to  oxidize 
chromium,  vanadium,  and  manganese.  After  10  min.  boiling, 
add  3  c.c.  of  3-normal  hydrochloric  acid  to  decompose  perman- 
ganic acid.  Boil  10  min.  longer,  cool,  add  25  c.c.  of  sulfuric 
acid,  and  titrate  afc  5°C.  with  a  ferrous  sulfate  solution  equivalent 
to  dichromate  solution  containing  0.001  g.  Cr  per  cubic  centimeter. 
The  titration  includes  chromium  and  vanadium.  Divide  the  tit- 
ration  by  3  and  multiply  by  2.943.  This  converts  both  chromium 
and  vanadium  into  the  equivalent  percentage  of  vanadium. 

To  a  second  100-c.c.  portion  add  a  few  cubic  centimeters  of 
ferrous  sulfate  solution  to  reduce  any  chromium  existing  in  the  oxi- 
dized condition  and  follow  this  with  20  c.c.  of  sulfuric  acid  and  40 
c.c.  of  nitric  acid  together  with  water  enough  to  give  a  volume  of 
200  c.c.  Evaporate  by  boiling  quietly  at  such  a  rate  that  in  one 
hour  the  volume  is  reduced  to  100  c.c.  Under  these  conditions 
99.5  per  cent  of  the  vanadium  is  oxidized.  Cool  to  5°C.  and  tit- 
rate with  ferrous  sulfate.  To  calculate,  divide  by  0.995  and  by  3 
and  multiply  by  2.943.  This  gives  the  percentage  of  vanadium. 

The  percentage  of  chromium  may  be  calculated  by  subtracting 
the  per  cent  obtained  by  the  second  oxidation  from  that  obtained 
by  the  first  and  dividing  the  difference  by  2.943. 

NOTES  AND  PRECAUTIONS. — In  oxidizing  with  ammonium  per- 
sulfate and  silver  nitrate  it  is  important  to  have  the  sulfuric 
acid  and  water  in  the  proportions  given.  After  adding  the 
ammonium  persulfate,  and  after  adding  the  hydrochloric  acid, 
the  solution  should  be  boiled  at  least  10  min. 


ELECTROMETRIC  METHODS  291 

The  concentration  of  nitric  acid,  the  initial  and  final  volumes, 
and  the  rate  of  evaporation  are  important  steps  in  securing  a 
regular  oxidation  of  vanadium  by  nitric  acid. 

Any  insoluble  matter  in  the  ferro-vanadium  suspected  of 
containing  vanadium  should  be  fused  with  sodium  peroxide. 
After  leaching  boil  the  alkaline  solution  for  20  min.  Then 
acidify  with  sulfuric  acid  and  add  to  the  main  portion  of  the 
solution  before  making  up  to  volume.  It  is  rare  that  this  treat- 
ment is  necessary. 

If  a  solution,  containing  2.883  g.  of  potassium  dichromate  in 
1  liter  should  be  used,  each  cubic  centimeter  would  correspond 
to  1  per  cent  of  vanadium  when  a  sample  weighing  3  g.  is  used. 

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ELECTROMETRIC  METHODS  293 

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ELECTROMETRIC  METHODS 


295 


THE  ELECTROMETRIC  DETERMINATION  OF  CARBON  IN 

STEEL1 

This  method  is  based  upon  the  measurement  of  the  change  in 
electrical  resistance  in  a  solution  of  barium  hydroxide  from  which 
a  part  of  the  barium  has  been  precipitated  as  carbonate  by  carbon 


g  100 

In  90 


Grctm<,  BA(OH)?  per  ZOOcc. 
?.0          3.0          4.0          5.0         6.0 


10 


90 


Cell  Constant 0.7 1 5 
Temperature  Z5°C 


15%  20% 

%  Carbon 


30% 


FIG.  42. 


dioxide  formed  by  direct  combustion  of  steel  in  an  electric  fur- 
nace. It  is  an  electrometric  method  because  the  final  estimation 
is  based  upon  two  measurements  of  electrical  resistance  but  it  is 
different  from  the  preceeding  methods  which  all  depended  upon 

^AIN  and   MAXWELL:  /.  I.   E.  C.,  11,  852  (1919);  Technologic  Paper 
No.  141,  U.  S.  Bureau  of  Standards. 


296 


CHEMICAL  ANALYSIS  OF  METALS 


the    measurement    of    electrode    potential.     The    fundamental 
chemical  reaction  involved  is 


Ba++  +  2OH 


BaCO3  +  H2O 


Barium  hydroxide  in  aqueous  solution  exists  chiefly  as  barium  and 
hydroxyl  ions  but  barium  carbonate  is  insoluble  ;  the  conductance 
of  the  solution,  which  is  the  reciprocal  of  the  resistance  value,  falls 
as  these  ions  are  removed.  The  temperature  of  the  solution  also 
has  a  marked  effect  upon  the  conductance,  changing  about  1.7 
per  cent  for  1°  of  temperature  change.  Figure  42  shows  the 


g 

x 

1 

\ 

N. 

\ 

4 

\ 

\ 

<y     7 

\ 

* 

\ 

•^o 

\ 

•fl'n 

V^ 

"~\^ 

E    7 

\ 

6    c 

\ 

g 

\ 

4 

> 

^ 

X 

^ 

\^ 

.1 

Vy 

^ 

4.0      4.1        4.1      4.1      4.4      4.5       4.6       4.1 
Cell  Constant  0.115  %  Carbon 

Temperature  25°C 

FIG.  43. 


4.8      4.9       5.0       5.1 


relation  between  the  electrical  resistance  and  barium  hydroxide 
concentration.1     The  curve  shows  that  these  changes  in  resistance 

1  The  bottom  values  for  the  abscissas  in  Fig.  42  are  expressed  in  what  Cain 
and  Maxwell  have  called  the  "equivalent  per  cent  carbon."  This  term  was 
chosen  for  convenience  in  using  a  nomograph  scale.  It  is  based  on  the 
assumption  that  exactly  200  c.c.  of  barium  hydroxide  solution  are  present 
in  the  absorption  tube,  which  is  also  used  for  the  resistance  measurement, 
and  that  a  sample  of  steel  weighing  exactly  2  g.  is  taken  for  analysis.  If  p 
represents  the  weight  of  Ba(OH)2  in  grams  present  in  the  solution,  then 

CXp  X  100  .    4,  ,       „ 

B  (OH)  X  2  1S  equivalent  per  cent  carbon." 


ELECTROMETRIC  METHODS 


297 


are  about  six  times  as  marked  for  corresponding  changes  in  con- 
centration on  the  portion  of  the  curve  lying  between  A  -B  as  on 
the  portion  C-D.  Solutions  to  the  left  of  A  contain  so  little 
barium  hydroxide  that  they  are  not  sufficiently  effective  as  absorb- 
ents for  carbon  dioxide. 

The  portion  of  the  curve  selected  for  use  by  this  method  is  again 
shown  in  Fig.  43  and  the  data  from  which  this  curve  was  drawn 
is  given  in  Table  1. 

TABLE   I. — DATA  FOR    RESISTANCE-CONCENTRATION  CURVE   OF  Ba(OH)2 

SOLUTIONS  IN  THE  REGION  4  PER  CENT  TO  5  PER 

CENT  CARBON  EQUIVALENT  STRENGTH 

CELL  CONSTANT  =  0.715 


Ba(OH)2  per 
200  c.c.  solution, 
grams 

Equivalent 
per  cent 
carbon 

Temperature 
degrees, 
Centigrade 

Observed 
resistance, 
ohms 

Corrected 
resistance, 
ohms 

.164 

4.075 

23.6 

100.9 

98.49 

.198 

4.194 

24.2 

97.4 

96.08 

.239 

4.337 

24.2 

94.6 

93.26 

.242 

4.348 

23.2 

95.8 

92.81 

.280 

4.482 

24.4 

91.4 

90.42 

.286 

4.500 

26.6 

87.6 

90.01 

.301 

4.553 

27.5 

85.3 

88.92 

.303 

4.559 

26.4 

86.8 

88.79 

.346 

4.712 

25.1 

86.0 

86.06 

.385 

4.848 

25.8 

82.7 

83.90 

.403 

4:912 

24.4 

84.2 

83.94 

.460 

5.110 

23.1 

82.8 

80.11 

The  resistance  of  barium  hydroxide  solutions  decreases  with 
rise  in  temperature.  Cain  and  Maxwell  have  determined  the 
resistances  of  barium  hydroxide  solutions  at  20°,  25°  and  30°  at 
concentrations  corresponding  to  approximately  4.0,  4.25,  4.50, 
4.75  and  5.0  equivalent  per  cent  carbon1  and  the  data  obtained  is 

1  When  the  concentration  of  the  barium  hydroxide  is  expressed  in  this 
way,  the  percentage  of  carbon  present  in  a  2-g.  sample  of  steel  is  found  by 
subtracting  the  "equivalent  carbon  concentration"  of  the  cell  after  the 
combustion  from  the  "equivalent  carbon  concentration"  at  the  start.  If 
a  2-g.  sample  of  steel  contained  5  per  cent  carbon  it  would  precipitate 
all  the  Ba(OH)2  in  200  c.c.  of  barium  hydroxide  solution  containing  5.0 
equivalent  per  cent  carbon. 


298 


CHEMICAL  ANALYSIS  OF  METALS 


given  in  Table  II.  The  values  for  a  and  /3  given  in  the  table  were 
obtained  by  substituting  the  experimental  temperatures,  t, 
and  resistances,  R,  in  the  equation 

JL       1   +  <*  [t  -  25]  +(3[t  -  25]2 

RT  ~  #23° 

TABLE  II. — DATA  FOR  TEMPERATURE  COEFFICIENTS  OF  RESISTANCE 


Concentration  of 
Ba(OH)2  solution 
per  cent 
Centigrade- 
approximate 

Temperature 
degrees 
Centigrade 

Resistance 
ohms 

a 

0  X  10~4 

5.00                        20 

135.25 

25 

124.02 

0.01674             0.2687 

30 

114.37 

4.75 

20 

142.18 

25 

130.36 

0.01680 

0.3505 

30 

120.16 

4.50 

20 

149.07 

25 

136.62 

0.01686 

0.3085 

30 

125.91 

4.25 

20 

156.18 

25 

143.07 

0.01687 

0.1652 

30 

131.89 

4.00 

20 

165.18 

25 

151.28 

0.01687 

0.0898 

30 

139.48 

If  the  temperature  of  the  solution  lies  between  15°  and  25° 
the  j3  term  in  the  correction  formula  can  be  neglected  but  this 
value  becomes  appreciable  if  the  solution  is  at  a  temperature 
is  more  than  10°  away  from  25°  which  is  chosen  as  a  suitable 
standard  temperature  in  this  method  of  analysis.  If  the  labora- 
tory temperature  is  above  35°  the  stock  bottle  14  in  Fig.  45 
should  be  placed  in  cold  water.  The  correction  formula  for 
changing  the  observed  resistance  value,  R,  to  that  which  would 
prevail  at  25°,  #25,  can  then  be  found  by  the  formula 
#25  =  Rt[l  +  a(t  -  25)]  in  which  a  =  0.0168 


ELECTROMETRIC  METHODS 


299 


The  simplest  way  of  determining  the  percentage  of  carbon 
equivalent  to  any  resistance  measurement  is  by  means  of  the 


-100 

-99 

-98 

•97 

-96 

-95 

-94 

•91 

•92 

•91 

-90 


-;  r3-90 
•(•4.00 
-4.10 


c  HH4.20 

O     J  L 


4-  1^4.40 

§  ir450 

^  Hh4.60 


HM.90 


-r35 


E^-33 


FIG.  44. — Nomograph  chart. 

nomograph  shown  in  Fig.  44,  p.     It  is  not  necessary,  here,  to 
go  into  the  mathematical  discussion  of  the  method  by  which 


300  CHEMICAL  ANALYSIS  OF  METALS 

this  scale  is  constructed  but  the  use  of  the  nomograph  is  very 
simple.  A  straight  edge  is  made  to  connect  the  observed  values 
for  temperature  and  resistance  and  the  intersection  with  the 
third  (middle)  ordinate  gives  the  concentration  of  the  solution 
in  terms  of  carbon  percentage;  this  may  be  termed  the  first 
concentration.  After  the  combustion  is  ended  a  similar  set  of 
readings  is  taken  and  subtraction  of  the  second  concentration 
reading  from  the  first  gives  directly  the  per  cent  of  carbon  if  a 
2-g.  sample  has  been  taken;  or,  if  a  1-g.  sample  has  been  used, 
the  result  is  multiplied  by  two.  The  scales  can  be  read  to 
0.005  per  cent  C,  0.05°C.,  and  0.05  ohm.  It  was  found  by 
comparison  of  chart  readings  in  a  number  of  cases  with  the 
resistances  computed  by  the  above  formula  that  the  error  of  the 
chart  is  less  than  0.005  per  cent  carbon. 

The  entire  apparatus  as  designed  by  Cain  and  Maxwell1  is 
shown  in  Fig.  45. 

The  outfit  consists  of  the  Hoskins  type  low-voltage  furnace 
(1),  fed  by  alternating  current  from  the  transformer  (2),  con- 
trolled by  the  rheostat  (3)  in  the  primary  circuit.  A  fused  silica 
combustion  tube  (4)  in  this  furnace  has  inserted  in  its  forward 
end  a  roll  of  80-mesh  copper  oxide  gauze  about  4  in.  long,  placed 
so  it  is  heated  by  conduction  from  the  hot  zone  'of  the  furnace 
to  from  300  to  400°C.  This  removes  sulphur  compounds  and 
also  ensures  complete  combustion  of  any  carbon  monoxide  that 
may  be  formed.  Oxygen  from  the  cylinder  (5)  passes  succes- 
sively through  the  reducing  valve  (6),  the  soda-lime  tower  (7) 
and  the  bubble  counting  device  (8),  into  the  furnace.  The  com- 
bustion is  made  in  nickel,  clay,  alundum,  platinum,  or  other  suit- 
able boats  filled  with  90-mesh  RR  Alundum,  Blue  Label,  sand. 
A  nickel  or  alundum  sleeve,  fitted  inside  the  tube  in  the  region 
occupied  by  the  boat,  protects  the  tube  from  spattered  oxides, 
or,  in  most  cases,  spattering  of  oxides  in  the  tube  can  be  pre- 
vented by  covering  the  steel,  after  placing  it  on  the  alundum  sand, 
with  some  more  of  the  alundum  sand.  Some  method  of  protec- 
tion of  the  tube,  such  as  recommended,  must  be  provided  in  order 
that  the  rapid  combustion  produced  by  the  procedure  described 
later  does  not  ruin  the  tube  by  the  throwing  off  of  fused  oxides. 

1  Loc.  tit.  The  illustration  and  description  of  the  apparatus  were  fur- 
nished by  the  A.  H.  Thomas  Co.  of  Philadelphia  for  use  in  this  book. 


ELECTROMETRIC  METHODS 


301 


The  oxygen  next  passes  into  the  absorption  vessels  through  stop- 
cocks (9).  The  absorption  vessels  (10)  and  10')  are  provided 
with  electrodes  (11)  and  (II7)  and  thermometers  (12)  and  (12'), 
and  are  connected  by  cocks  (13)  and  (13')  with  the  reservoir  (14) 
containing  stock  barium  hydroxide  solution,  and  with  bottle  (15) 
which  receives  used  or  spent  solution.  Filling  and  emptying  of 


FIG.  45. 

absorption  tubes  must  in  all  cases  be  done  through  stopcocks 
(13)  and  (13').  In  no  case  must  the  covers  (16)  and  (16')  be 
removed  for  filling  and  emptying,  nor  must  the  absorption  ves- 
sels be  removed  from  the  support  (17).  This  is  very  important. 
The  electrodes  of  the  absorption  vessels  are  connected  through 
the  double-throw  switch  (18)  with  the  binding  posts  (19)  of  the 
special  resistance  measuring  bridge  (20) .  The  other  two  binding 


302  CHEMICAL  ANALYSIS  OF  METALS 

posts  (21)  of  this  bridge  are  connected  through  the  switch  (22) 
with  a  110-volt  alternating  current  line  (25  or  60-cycle).  The 
bulbs  (10)  and  (100  of  the  absorption  vessels  are  fitted  with 
single  perforated  rubber  stoppers,  carrying  tube  (23)  and  (23'). 
A  rubber  tube  connected  to  a  soda-lime  tower,  which  in  turn  is 
connected  to  the  laboratory  air  supply,  can  be  slipped  alter- 
nately on  to  either  of  these  glass  tubes  or  the  arm  (24)  of  stop- 
cock (9). 

Procedure. — The  two  absorption  vessels  are  filled  to  the  200- 
c.c.  mark  with  barium  hydroxide  solution  from  the  stock  bottle 
14,  Fig.  45.  Oxygen  or  air  freed  from  carbon  dioxide  is  passed 
for  a  few  seconds  to  mix  the  solutions,  and  their  temperatures 
and  resistances  are  then  recorded.  In  the  meantime  the  com- 
bustion boat  filled  with  alundum  sand  has  been  preheating  in  the 
furnace,  which  for  this  work  should  be  maintained  continuously 
at  1,050  to  1,100°C.,  preferably  the  latter  temperature.1  This 
is  an  extremely  important  point,  for  if  the  temperature  is  too 
low  or  the  oxygen  is  not  pure  or  is  not  admitted  at  300  to  400  c.c. 
per  minute  after  the  combustion  starts,  the  rapid  combustion 
essential  to  successful  absorption,  can  not  be  secured.  The  boat 
is  removed  from  the  furnace,  and  when  at  a  low-red  heat  the 
sample  is  distributed  on  the  alundum2  and  the  boat  replaced  in 
the  furnace  and  left  to  preheat,  without  oxygen  passing,  while 
the  next  sample  is  being  weighed.  Oxygen  is  now  passed  at  the 
rate  of  300  to  400  c.c.  per  minute  for  the  next  2  min.;  then  stop- 
cock 13,  Fig.  45,  is  turned  to  position  2,  which  admits  carbon- 
dioxide-free  air;  this  should  pass  at  the  same  rate  as  the  oxygen. 
During  this  combustion  period,  if  directions  have  been  followed, 
all  carbon  dioxide  will  have  been  removed  from  the  furnace,  but 
some  still  remains  in  the  large  bulb  of  the  absorption  apparatus ; 
the  air  removes  this.  The  advantage  of  the  use  of  air  at  this 
stage  is  obvious :  a  saving  of  oxygen  is  effected  and  the  furnace  is 
immediately  available  for  burning  the  next  sample.  While  air 

1  The  melting  point  of  gold  is  a  convenient  temperature  check.     If  this 
metal  is  not  melted  the  temperature  is  too  low.     See  cited  paper  by  Cain 
and  Maxwell. 

2  Experience  has  shown  that  no  loss  of  carbon  occurs  unless  the  sample 
contains  dust;  with  most  steels  this  can  first  be  removed  without  causing 
an  error  in  the  carbon  determination.     This  point  should  always  be  tested, 
however,  in  burning  new  steels. 


ELECTROMETRIC  METHODS  303 

is  passing  through  the  first  tube  (1%  to  2  min.  is  necessary  for 
this)  the  combustion  of  the  next  sample  proceeds  as  already 
directed,  using  the  second  absorption  tube.  The  second  reading 
of  resistance  and  temperature  on  the  first  tube  then  follows,  and 
if  the  solution  is  not  too  dilute  it  can  be  used  for  absorbing  the 
carbon  dioxide  from  other  samples ;  otherwise,  a  little  is  allowed 
to  flow  into  the  reservoir  G,  and  the  tube  filled  to  the  mark  again 
with  fresh  solution.  Of  course  it  is  an  economy  in  time  for  the 
operator,  wherever  possible,  to  choose  conditions  (weight  of 
sample,  carbon  content  of  same,  etc.)  so  as  to  get  the  maximum 
number  of  determinations  for  a  single  filling,  since  in  this  way 
the  second  resistance  and  temperature  readings  serve  as  initial 
values  for  the  next  combustion,  and  so  on.  The  solution  should 
not  be  used  when  it  is  more  dilute  than  corresponds  to  4  per  cent 
carbon  (i.e.,  99.5  ohms  at  25°;  see  nomograph,  Fig.  44,  for  the 
limiting  resistances  corresponding  to  other  temperatures),  since 
its  absorptive  power  at  rapid  rates  of  passage  of  the  oxygen  is 
then  less,  and  some  carbon  dioxide  may  be  lost.  The  data  re- 
lating to  combustions  should  be  recorded  as  obtained.  It  is 
convenient  to  use  a  tabular  form  or  record  showing  (1)  desig- 
nation of  sample,  (2)  weight  taken,  (3)  cell  used,  (4)  initial  tem- 
perature, (5)  final  temperature,  (6)  initial  resistance,  (7)  final 
resistance,  (8)  initial  concentration,  (9)  final  concentration,  (10) 
carbon  percentage  in  sample,  and  (11)  remarks.  There  is  ample 
time  for  entering  this  information  while  other  operations  are 
going  on.  A  very  good  way  is  to  enter  "  final  temperature " 
below  " initial  temperature,"  and  "final  resistance"  after  "initial 
resistance  "  for  each  sample,  since  this  relates  these  quantities  in 
an  easy  manner  for  reading  the  nomograph. 

The  speed  of  the  method  naturally  depends  on  the  skill  of  the 
operator  and  the  ingenuity  displayed  in  arranging  a  cycle  of 
operations  which  secures  the  best  speed  under  his  working  condi- 
tions. Operators  when  working  on  a  series  of  Bureau  of  Stand- 
ards analyzed  samples  averaged  one  determination  per  4J£  to 
5  min.  The  accuracy  of  results  is  shown  in  Table  III. 


304  CHEMICAL  ANALYSIS  OF  METALS 

TABLE  111. — RESULTS  BY  ELECTROLYTIC  RESISTANCE  METHOD 


Sample  used 

Grams  used 

Bureau  of 
Standards 
value  for 
carbon  f  av- 
erage by 
direct  com- 
bustion), 
per  cent 

Value  by 
electrolytic 
resistance 
method 

Analyst 

lla  

2.0 

, 

ro.2i 

. 

Ha  

2.0 

>  0  .  223 

i 

10.21 

y  Maxwell. 

12h 

r2.0 
<{  2  0 

[o  409 

r  0.41 
\  0  41 

[  Swindells 

14a 

ll.O 

r2.0 
1  0 

I  0.813 

I  0.42 

f  0.81 
1  0  82 

i  Swindells. 

16a 

12.0 

0.5 
0.5 
1  0 

1 
0.990 

10.80 

1.00 
1.00 
1  00 

Maxwell. 
Cain. 

21a          

2.0 

2.0 

0.98 
fO.62 

Cain. 

21a 

2  0 

JO.  617 

< 
10  62 

Maxwell. 

Sugar  (grams  carbon). 

f     ° 

0. 

1          0. 

00421 
00421 
00421 

0.0046 
0.0042 
0.0040 

Maxwell. 

OPERATING  SUGGESTIONS 

1.  Stock  barium  hydroxide  solutions  are  conveniently  made 
in  one  to  two  carboy  lots  by  adding  solid  barium  hydroxide  to 
the  carboy  nearly  filled  with  water  (agitating  with  air)  until  the 
equivalent  strength  approaches  5  per  cent  carbon.  Subsequent 
additions  can  then  be  made  by  adding  a  saturated  barium 
hydroxide  solution.  Of  course,  it  is  not  necessary  to  make  up 
exactly  to  the  equivalent  of  5  per  cent  carbon.  An  approxima- 
tion to  this  is  all  that  is  desired.  The  strength  of  the  solution  is 
determined  from  time  to  time  during  the  standardization  by 
running  a  portion  of  the  solution  into  the  cell  and  measuring  its 
resistance.  If  a  setup  like  that  shown  in  Fig.  45  is  used  in 
measuring  the  resistance,  it  is  not  necessary  to  remove  bottle  14 
from  the  shelf  or  to  break  any  of  the  connections  during  these 
operations.  If  it  is  desired  to  economize  in  the  use  of  barium 
salt,  the  waste  solution  in  bottle  15  can  be  brought  up  to  strength 


ELECTROMETRIC  METHODS 


305 


as  described,  after  first  decanting  it  off  from  the  barium  carbonate 
that  has  settled  out.  A  still  further  economy  can  be  effected 
by  drying  and  calcining  to  oxide  the  precipitated  barium  carbon- 
ate. This  oxide  can  then  be  used  again. 

2.  The  cell  constants  should  be  checked  from  time  to  time. 
This  may  be  done  (1)  by  burning  standard  samples  or  (2)  by 
determining  the  resistance  of  a  N/10  solution  of  pure  potassium 
chloride.  This  solution  should  be  prepared  on  the  day  it  is  to 
be  used,  since  stock  solutions  have  been  found  to  change  during 
the  course  of  this  work.  Table  IV  shows  the  resistivities  at 

TABLE  IV. — SPECIFIC  RESISTIVITY  OF  N/10  KC1  SOLUTION  AT  VARIOUS 

TEMPERATURES 

(From  Landolt-Bornstein  Physik.  Chemische  Tabellen  4  Ed.,  p.  1117.) 


Temperature 

Resist- 
ance, 
ohms 

Temperature 

Resist- 
ance, 
ohms 

Temperature 

Resist- 
ance, 
ohms 

15  0 

95  42 

22  0  

82.30 

29.0  

72.10 

16.0  
17  0 

93.28 
91.32 

23.0  
24.0  

80.71 
79.11 

30.0  
31.0  

70.82 
69.59 

18  0 

89  37 

25  0 

77  64 

32  0 

68  40 

19.0  
20  0 

87.49 
85  69 

26.0  
27  0 

76.16 
74  79 

33.0  
34  0 

67.20 
66  09 

21  0  

83.96 

28.0  

73.42 

35.0  

64.98 

various  temperatures  of  N/10  potassium-chloride  solutions.     The 

r> 

cell  constant  is  computed  from  the  formula :  R  =  NS,  or  N  =  -« 

where  R  is  the  observed  resistance,  N  the  cell  constant,  and  S  the 
resistivity,  taken  from  Table  IV,  for  the  same  temperature.  If 
a  change  in  cell  constant  has  taken  place,  it  is  most  probable 
that  the  electrodes  need  replatinizing.  Directions  for  this  are 
given  in  paragraph  4  of  this  section.  If  Method  1  is  used,  any 
marked  deviation  from  the  correct  carbon  value  of  the  standard 
steel  may  be  due  to  a  change  in  the  cell  constant,  and  this  should 
then  be  checked  by  Method  2,  unless  it  is  suspected  that  the  error 
in  the  carbon  determination  is  due  to  some  other  cause.  No 
deviation  of  cell  constants  has  been  observed  until  after  several 
months'  use,  and  then  the  change  is  sudden  and  erratic.  When 
20 


306  CHEMICAL  ANALYSIS  OF  METALS 

the  cell  constant  changes,  it  should  be  brought  back  to  the 
original  value. 

The  adjustment  of  the  cell  constant  is  made  by  moving  the 
electrodes  up  and  down  after  loosening  the  stuffing  box;  a  marked 
change  takes  place  as  they  approach  the  meniscus. 

3.  If  the  absorption  vessels  are  not  to  be  used  for  some  time, 
they  should  be  cleaned  with  hydrochloric  acid  (not  over  2  to  3 
per  cent  HC1)  followed  by  distilled  water.     Extreme  care  should 
be  taken  that  none  of  the  hydrochloric  acid  or  chlorides  enter  the 
reservoir  for  waste  barium  hydroxide  solution  if  this  is  to  be  used 
again. 

4.  To  platinize  the  electrodes,  the  cap  carrying  them  is  removed 
from    the    cell,    and    they    are    first    cleaned    with    sulphuric 
and   chromic-acid   mixture,   followed  by  distilled  water.     Then 
they  are  immersed  in  a  vertical  position  in  a  solution  made  of 
100  g.  water,  3  g.  chloroplatinic  acid,  and  0.02  to  0.03  g.  lead 
acetate.     Current  is  passed  through  the  solution  by  connecting 
the  electrodes  to  three  dry  batteries  in  series.     The  current  is 
passed   for   5  min.,  reversing  every  half  minute.     Finally,  an 
auxiliary  platinum  electrode  is  introduced  and  current  passed 
with  this  as  anode  for  another  2  min.,  after  which  the  electrodes 
are  washed  thoroughly  with  distilled  water  and  are  then  ready 
for  use. 


CHAPTER  XXII 
NON-FERROUS  ALLOYS 

The  preceding  chapters  have  dealt  with  the  analysis  of  ferrous 
alloys  and  the  methods  described  were  applicable  to  the  estima- 
tion of  small  quantities  of  various  elements  in  the  presence  of  a 
large  quantity  of  iron.  In  the  analysis  of  commercial  copper 
alloys,  the  quantity  of  iron  present  has  little  if  any  effect  upon 
the  determination  of  the  other  constituents.  Moreover,  in  the 
analysis  of  copper  alloys  special  emphasis  is  placed  upon  the 
quantitative  determination  of  the  most  important  constituents, 
whereas  in  the  analysis  of  iron  and  steel  the  quantity  of  iron  pres- 
ent is  rarely  determined  by  direct  analysis. 

Brass  is  an  alloy  of  copper  and  zinc  and  many  samples  of  brass 
contain  less  than  one-tenth  of  1  per  cent  of  other  constituents. 
The  copper  and  zinc  used  to  make  the  alloy,  however,  are  never 
absolutely  pure  and  brass  usually  contains  traces  of  lead,  tin, 
cadmium,  arsenic,  iron,  etc.  Bronze  is  usually  defined  as  an 
alloy  of  copper  and  tin  but  other  elements  are  often  added  inten- 
tionally and  certain  alloys  which  look  like  bronze  have  been 
classified  as  such  although  they  may  contain  no  tin.  Thus 
aluminium  bronze  is  copper  alloyed  with  5  to  10  per  cent  of 
aluminium.  Phosphor-bronze,  on  the  other  hand,  is  a  copper- 
tin  alloy  to  which  a  little  phosphorus  has  been  added  inten- 
tionally and  manganese  bronze  is  a  copper-tin  alloy  to  which 
manganese  has  been  added. 

Inasmuch  as  small  quantities  of  antimony  are  likely  to  be 
present  in  commercial  brasses  and  bronzes  it  has  seemed  advisable 
to  extend  this  chapter  somewhat  and  include  the  analysis  of  a 
typical  tin-antimony  alloy  in  which  the  copper  content  is  low. 

Copper  is  so  far  below  hydrogen  in  the  electrochemical  series 
of  the  elements  that  it  does  not  dissolve  in  dilute  hydrochloric 
or  sulfuric  acid1  unless  some  other  substance  is  present  containing 

1  Copper  reacts  with  hot,  concentrated  sulfuric  acid  to  form  cupric  sul- 
fate  and  sulfur  dioxide.  In  this  case,  the  sulfate  ion  acts  as  oxidizing 
agent. 

Cu  +  2H2SO4-*CuSO4  +  2H2O  +  SO2 1 
307 


308  CHEMICAL  ANALYSIS  OF  METALS 

an  ion  which  has  greater  oxidizing  power  than  the  hydrogen 
ion. 

The  most  appropriate  solvent  for  copper  and  its  alloys  is 
nitric  acid.  The  copper  is  oxidized  to  the  cupric  condition  and 
the  nitrate  ion  is  reduced.  If  an  excess  of  concentrated  nitric 
acid  is  used,  nitrogen  peroxide  is  the  principal  reduction  product, 
but  with  dilute  nitric  acid,  nitric  oxide  is  formed: 

Cu  +  2NO3~  +  8H+->  Cu++  +  2NO  T  +  4H3O 

The  equation  written  in  this  form  shows  that  eight  molecules  of 
nitric  acid  are  required  to  react  with  1  atom  of  copper  but  that 
only  two  molecules  of  nitric  acid  act  as  oxidizing  agent. 

The  behavior  of  tin  and  antimony  toward  nitric  acid  is  charac- 
teristic. Cold,  dilute  nitric  acid  dissolves  tin  slowly,  forming 
stannous  and  ammonium  nitrates: 


3Sn  +  20NO3~  +  10H+-+3Sn++  +  NH4+  +  3H2O 

With  hot,  6-normal  nitric  acid  (d.  1.2)  stannic  nitrate  is  formed 
but  this  undergoes  hydrolysis  and  "metastannic  acid"  is 
precipitated.  The  entire  reaction  may  be  expressed  as  follows  : 

15Sn  +  20NOr  +  20H+  +  5H2O-»3(H2SnO3)5  +  20NO  T 

Stannic  hydroxide  is  an  insoluble,  amphoteric  substance  with 
colloidal  properties.  When  formed  by  the  addition  of  caustic 
alkali  to  the  solution  of  a  stannic  salt,  it  probably  corresponds  to 
the  composition,  Sn(OH)4,  and  in  this  condition  it  dissolves 
readily  in  hydrochloric  acid  and  in  caustic  alkali  soltuion.  By 
drying  over  sulfuric  acid  it  becomes  changed  to  a-metastannic 
acid,  H2SnO3,  and  this  compound  in  acid  solution  polymerizes  into 
/3-metastannic  acid,  (H2SnO3)5.  In  the  last-mentioned  condition, 
stannic  hydroxide  is  least  soluble  in  acid  and  in  alkali.  The  pre- 
cipitate produced  by  boiling  tin  with  moderately  concentrated 
acid  contains  nitric  acid  and  appears  to  correspond  to  the  formula 
Sn5O5(OH)8(NO3)2  but  by  washing  with  water  the  nitric  acid 
can  be  removed1  and  the  precipitate  then  corresponds  to  the 
formula,  (H2Sn03)5  which  may  be  written: 

Sn505(OH)10 
1  c/.  A.  KLEINSCHMIDT,  Monatsh,  39,  14&-78  (1918). 


NON-FERROUS  ALLOYS  309 

The  behavior  of  antimony  to  nitric  acid  is  similar.  Antimonic 
hydroxide  is  amphoteric,  insoluble  and  colloidal.  The  precipitate 
formed  by  treating  antimony  with  nitric  acid  is  antimony 
tetroxide,  Sb2O4,  and  may  be  regarded  as  antimonous  antimon- 

/o\ 

ate,  Sb— O— Sb=O. 
\0/ 

If  an  alloy  dissolves  completely  in  nitric  acid,  and  no  precipi- 
tate forms  upon  heating  the  solution,  it  is  safe  to  assume  that 
antimony  and  tin  are  absent.  When  tin  or  antimony  is  present, 
however,  the  precipitated  metastannic  acid  or  antimony  tetroxide 
is  rarely  pure.  These  colloidal  precipitates  have  the  property  of 
adsorbing  dissolved  substances  to  a  marked  degree.  Thus 
phosphoric  and  arsenic  acids  are  adsorbed  and  are  to  be  found  in 
the  residue  when  antimony  or  tin  is  present.  To  a  lesser  degree 
other  elements,  such  as  titanium,  iron  and  even  copper,  are  likely 
to  be  adsorbed. 

The  colloidal  properties  of  metastannic  acid  not  only  explain 
why  it  is  rarely  obtained  pure  as  a  result  of  dissolving  an  alloy 
in  nitric  acid  but  they  also  account  for  the  fact  that  certain 
substances  interfere  with  the  formation  of  the  gelatinous  precipi- 
tate and  tend  to  keep  it  in  solution.  Hydrochloric  acid  is  one  of 
the  most  efficient  means  of  causing  the  "  peptonization "  or 
dissolving  of  the  precipitate  but  small  quantities  of  iron  have  also 
been  found  to  prevent  complete  precipitation.  It  has  been 
stated,  for  example,  that  the  precipitation  of  metastannic  acid 
is  never  complete  if  the  original  alloy  contains  as  much  as  0.25 
per  cent  of  iron. 

The  quantitative  estimation  of  aluminium,  antimony,  arsenic, 
copper,  iron,  lead,  manganese,  nickel,  phosphorus  and  zinc 
in  typical  " non-ferrous  alloys"  will  be  discussed  in  this  chapter, 
the  term  "  non-ferrous  "  being  used  merely  to  contrast  the  alloys 
with  those  in  which  iron  is  the  basic  constituent.  In  previous 
chapters  the  determination  of  each  constituent  has  been  discussed 
for  the  most  part  without  regard  to  whether  the  same  weighed 
portion  of  metal  can  be  used  for  the  determination  of  several 
constituents.  In  the  analysis  of  non-ferrous  alloys,  it  is  the 
exception  rather  than  the  rule  when  one  portion  of  the  material 
is  used  for  only  one  determination.  In  prescribing  directions  for 


310  CHEMICAL  ANALYSIS  OF  METALS 

analysis,  therefore,  it  is  necessary  not  only  to  bear  in  mind  the 
possibility  of  interference  due  to  the  presence  of  other  constitu- 
ents but  also  to  consider  whether  these  other  constituents  had 
best  be  removed  previously  or  subsequently.  Owing  to  this 
dependence  of  one  determination  upon  another  it  has  been  difficult 
to  decide  upon  a  wholly  logical  order  of  treatment  and  it  was 
finally  decided  to  discuss  the  above  ten  elements  in  alphabetical 
sequence  but  this  involves  the  analysis  of  metal  containing 
elements  to  be  discussed  later,  so  that  the  order  is  not  followed 
strictly. 

ALUMINIUM 

The  metal  aluminium  is  dissolved  by  dilute  hydrochloric  acid, 
forming  aluminium  chloride,  but  it  is  less  soluble  in  dilute  sulfuric 
acid  and  becomes  passive  when  treated  with  nitric  acid,  probably 
because  a  closely  adherent  oxide  film  is  formed  by  the  action  of 
nitric  acid.  Aluminium  dissolves  easily  in  caustic  alkali  solution 
forming  sodium  or  potassium  aluminate.  Many  schemes  of  an- 
alyzing commercial  aluminium,  or  an  alloy  in  which  aluminium 
forms  the  major  constituent,  are  based  upon  preliminary  treat- 
ment with  sodium  hydroxide  to  dissolve  the  aluminium  and  zinc; 
this  leaves  most  of  the  other  constituents  in  the  insoluble  residue. 
The  determination  of  aluminium  in  ferrous  alloys  has  been  dis- 
cussed in  Chap.  XIV.  It  will  lead  us  too  far  to  consider  the 
analysis  of  commercial  aluminium  ware  or  of  alloys  containing 
high  percentages  of  aluminium.  Here,  merely  a  method  for  the 
analysis  of  aluminium  bronze  will  be  described. 

ANALYSIS  OF  ALUMINIUM  BRONZE 

Procedure. — Dissolve  1  g.  of  the  alloy  in  10  c.c.  of  aqua  regia. 
To  the  resulting  solution  add  5  c.c.  of  concentrated  sulfuric  acid 
and  evaporate  till  heavy  fumes  are  obtained.  Cool,  dilute  to 
about  50  c.c.,  boil  until  the  sulfates  have  all  dissolved,  filter  and 
wash  thoroughly  with  hot  water.  The  residue  on  the  filter  paper 
is  usually  silica  which  can  be  ignited  and  weighed. 

Remove  the  copper  by  electrolysis  as  described  below  under 
Copper. 

To  the  filtrate  add  2  or  3  g.  of  disodium  phosphate  and  ammo- 
nium carbonate  solution  until  a  small  permanent  precipitate  is 


NON-FERROUS  ALLOYS  311 

obtained.  Dissolve  this  precipitate  by  adding  a  few  drops  of 
hydrochloric  acid  and  add  about  1  c.c.  of  6-normal  acid  in  excess. 
Dilute  to  300  c.c.,  add  5  g.  of  sodium  thiosulfate  and  heat  to 
boiling.  Add  20  c.c.  of  6-normal  acetic  acid,  boil  10  min.,  to 
coagulate  the  sulfur  and  filter.  Wash  the  precipitate  with  hot 
water  until  the  washings  give  no  test  for  chloride.  Ignite  and 
weigh  as  A1PO4  containing  22.19  per  cent  Al. 

This  method  of  precipitation  has  been  explained  in  Chap.  XIV. 

ANTIMONY 

The  proper  solvent  for  antimony  and  its  alloys  is  aqua  regia 
by  which  it  is  converted  into  chloride.  Nitric  acid,  as  already 
explained,  converts  antimony  into  Sb2O4  which  dissolves  slightly 
in  concentrated  acid  but  is  practically  insoluble  in  dilute  nitric 
acid.  The  antimony  present  in  alloys  containing  small  quantities 
of  this  element  may  be  determined  in  the  residue  obtained,  as  in 
the  analysis  of  bronze,  by  treatment  with  nitric  acid.  The 
separation  of  antimony  from  copper  and  similar  metals  can 
also  be  effected  by  taking  advantage  of  the  fact  that  antimony 
sulflde,  although  insoluble  in  dilute  acids,  dissolves  in  alkali 
sulfide  solution,  or  more  readily  in  alkaline  polysulfide,  forming, 
in  the  latter  case,  alkali  thioantimonate.  The  gravimetric 
separation  of  antimony  and  tin  is  usually  based  upon  the  fact 
that  antimony  sulfide  is  precipitated  more  readily  than  tin 
sulfide  from  acid  solutions.  Thus  the  classic  method  of  F.  W. 
Clarke  is  based  upon  the  precipitation  of  antimony  sulfide  from 
a  solution  containing  oxalic  acid. 

Antimony  may  be  determined  electrolytically,  gravimetrically 
or  volumetrically.  The  electrolytic  method  depends  upon  the 
deposition  on  the  cathode  from  a  sodium  sulfide  solution  to 
which  some  such  substance  as  potassium  cyanide  is  added  to 
react  with  polysulfides  formed  at  the  anode.  The  gravimetric 
determination  is  based  upon  the  ignition  of  a  pure  antimony 
sulfide  precipitate  in  a  stream  of  carbon  dioxide  gas  at  about 
230°;  in  this  way  dry  Sb2S3  is  obtained.  The  volumetric  deter- 
mination may  be  based  upon  (a)  the  oxidation  of  antimony  from  the 
trivalent  condition  to  the  quinquevalent  condition,  by  treatment 
with  potassium  permanganate  if  the  titration  is  done  in  acid 
solution  or  by  iodine  in  neutral  solution  or  (b)  upon  the  reduction 


312  CHEMICAL  ANALYSIS  OF  METALS 

of  quinquevalent  antimony  by  potassium  iodide  in  acid  solution 
and  titration  of  the  liberated  iodine  with  sodium  thiosulf  ate.  It  is 
interesting  to  note  that  when  antimony  pentasulfide  dissolves  in 
hydrochloric  acid,  antimony  trichloride  is  formed  which  unites  with 
hydrochloric  acid  to  form  soluble  complexes.  In  an  acid  solution 
tin  is  much  more  readily  oxidized  than  antimony.  By  dissolving 
a  mixture  of  antimony  and  tin  in  hot  sulfuric  acid  and  shaking  in 
the  air,  the  tin  is  oxidized  to  the  stannic  condition  and  the 
antimony  left  as  trivalent  salt.  Metallic  antimony  is  often 
added  to  reduce  tin  from  the  stannic  to  stannous  condition  and 
in  the  resulting  acid  solution  tin  can  be  oxidized  by  iodine  without 
affecting  the  antimony  trichloride  present.  To  illustrate  the  deter- 
mination of  antimony  in  alloys  two  methods  for  the  examina- 
tion of  bearing  metal,  or  an  alloy  of  lead,  tin,  antimony  and 
copper  will  be  described.1 

ANALYSIS  OF  BEARING  METALS 

As  solvent  for  the  alloy,  prepare  the  following  solution:  Dis- 
solve 20  g.  of  potassium  chloride  in  500  c.c.  of  water,  mix  with 
40  c.c.  of  concentrated  hydrochloric  acid  and  add  100  c.c.  of 
concentrated  nitric  acid.  Dissolve  1  g.  of  the  finely  divided 
alloy  in  70  to  100  c.c.  of  the  solvent,  heating  to  near  the  boiling 
point.  Boil  gently  until  the  metal  is  all  dissolved  and  the  volume 
of  the  solution  is  reduced  to  50  c.c.  Add  5  c.c.  of  concentrated 
hydrochloric  acid  and  cool  by  placing  the  beaker  in  cold  water. 
When  most  of  the  lead  has  precipitated  as  lead  chloride,  prefer- 
ably after  standing  over  night,  slowly  add  50  c.c.  of  95  per  cent 
alcohol  while  constantly  stirring.  Continue  stirring  a  few 
minutes  and  place  the  beaker  in  ice  water  for  10  min.  Add  50  c.c. 
more  of  alcohol  in  the  same  way  as  before  and  allow  to  stand 
20  min.  in  ice  water.  Filter  through  a  9-cm.  filter  into  an  800-c.c. 
beaker.  Wash  three  times  by  decantation  with  a  mixture  of 
concentrated  hydrochloric  acid  and  four  times  as  much  alcohol. 
The  precipitate  contains  all  but  about  3  mg.  of  the  total  lead 
content.  Ordinarily,  this  correction  may  be  applied  without 
attempting  to  recover  the  last  traces  of  lead. 

Preserve  the  filtrate  for  the  determination  of  antimony,  copper 
and  tin. 

1  The  methods  are  recommended  by  the  American  Society  for  Testing 
Materials. 


NON-FERROUS  ALLOYS  313 

Determination  of  Lead. — Wash  the  lead  chloride  back  into  the 
original  beaker  and  thoroughly  wash  the  filter  paper  with  hot 
water  and  then  twice  with  hot  ammonium  acetate  solution 
(1  vol.  cone,  ammonium  hydroxide  +  1  vol.  water  +  80  per  cent 
acetic  acid  until  the  solution  is  barely  acid  to  litmus).  A  clear 
solution  should  be  obtained;  as  little  as  1  mg.  of  tin  or  antimony 
will  cause  turbidity.  Add  15  c.c.  of  saturated  potassium  dichro- 
mate  solution,  heat  until  the  precipitated  lead  chromate  is  of  a 
good  orange  color,  filter  into  a  weighed  Gooch  crucible  and 
wash  with  water  and  dilute  alcohol.  Dry  at  110°  and  weigh. 
Calculate  to  lead  by  the  empirical  factor  0.6375. 

Precipitation  of  Copper  and  Antimony. — Evaporate  the  filtrate 
from  the  lead  chloride  to  dryness.  Add  2  g.  of  solid  potassium 
hydroxide  dissolved  in  10  c.c.  of  water  and  after  a  few  minutes 
add  20  c.c.  of  3  per  cent  hydrogen  peroxide.  Test  the  solution 
with  litmus  to  make  sure  that  it  is  alkaline  and  heat  on  the  water 
bath  for  20  min.  Add  10  g.  of  ammonium  oxalate,  10  g.  of 
oxalic  acid  and  200  c.c.  of  water.  Boil  and  introduce  hydrogen 
sulfide  into  the  hot  solution  for  45  min.  This  serves  to  precipi- 
tate the  antimony  and  tin  as  sulfides  leaving  the  tin  in  solution. 
The  lead  which  was  not  precipitated  as  lead  chloride  is  usually 
precipitated  as  sulfide  at  this  stage,  but  if  only  a  little  copper  or 
antimony  is  present,  it  may  remain  in  solution  with  the  tin. 
Filter  and  wash  the  sulfides  of  antimony  and  copper  with  hot 
water  containing  hydrogen  sulfide. 

Determination  of  Tin. — Concentrate  the  filtrate  to  about 
100  c.c.  and  if  more  than  0.5  g.  of  tin  is  present,  add  5  g.  more  of 
oxalic  acid.  Electrolyze  over  night  with  a  gauze  cathode  and 
a  current  of  about  0.5  ampere.  If  the  solution  is  alkaline  in  the 
morning,  the  tin  is  probably  all  precipitated,  but  tin  is  not 
deposited  well  from  an  alkaline  solution.  Remove  the  electrode, 
wash  with  water  and  alcohol,  dry  at  100°  and  weigh  as  metallic  tin. 
Add  5  g.  of  oxalic  acid  to  the  electrolyzed  solution,  heat  to  boiling 
and  again  electrolyze  to  see  if  any  tin  was  left  in  the  solution. 

Determination  of  Copper. — Wash  the  precipitated  antimony 
and  copper  sulfides  back  into  the  beaker  in  which  the  precipita- 
tion took  place,  using  as  little  water  as  possible.  Add  2  g.  of 
potassium  hydroxide  dissolved  in  10  c.c.  of  water.  Heat  until  the 
insoluble  residue  of  copper  sulfide  is  distinctly  black  and  then 


314  CHEMICAL  ANALYSIS  OF  METALS 

filter  through  the  same  filter  that  was  used  to  collect  the  precipi- 
tate of  copper  and  antimony  sulfides,  catching  the  filtrate  in  a 
300-c.c.  Erlenmeyer  flask.  The  copper  is  now  on  the  filter  as 
copper  sulfide  and  the  antimony  is  in  the  filtrate  and  as  potassium 
thioantimonate.  The  copper  sulfide  precipitate  usually  contains 
a  little  lead  sulfide.  Ignite  the  precipitate  and  filter  in  a  porce- 
lain crucible  and  dissolve  the  oxides  in  2  c.c.  of  6-normal  nitric 
acid.  Dilute  the  solution  to  50  c.c.  and  determine  the  copper 
(and  lead)  as  described  under  Copper. 

Determination  of  Antimony. — The  solution  of  potassium  thio- 
antimonate obtained  by  the  above  treatment  should  not  exceed 
40  c.c.  in  volume.  Add  50  c.c.  of  concentrated  hydrochloric  acid 
and  boil  for  a  few  minutes  to  volatilize  any  arsenic  as  trichloride. 
The  antimony  chloride  is  left  in  the  trivalent  condition  in  the 
form  of  a  complex  such  as  HSbCl4.  The  hydrogen  sulfide  from 
the  decomposition  of  the  thioantimonate  serves  to  reduce  traces 
of  arsenic  to  the  trivalent  condition.  Add  25  c.c.  more  of  hydro- 
chloric acid  and  1  g.  of  potassium  chlorate.  Boil  until  the  solu- 
tion is  colorless  and  the  chlorine  dioxide  is  all  expelled.  Filter 
through  mineral  wool  into  another  300-c.c.  flask  if  sulfur  has 
deposited  and  wash  the  original  flask  and  the  mineral  wool  with 
concentrated  hydrochloric  acid.  The  antimony  is  in  the  quin- 
quevalent  condition  after  boiling  with  the  potassium  chlorate. 

Cool  the  solution  to  room  temperature,  or  lower,  and  add  2  g. 
of  potassium  iodide  and  1  c.c.  of  carbon  tetrachloride.  Titrate 
slowly  with  tenth-normal  sodium  thiosulfate  solution  until,  after 
shaking,  the  violet  color  is  no  longer  visible  in  the  carbon  tetra- 
chloride. One  cubic  centimeter  of  tenth-normal  Na2S203  = 
0.0060  g.  of  Sb. 

The  reactions  that  take  place  with  the  antimony  throughout 
this  analysis  may  be  represented  by  the  following  equations. 

3Sb  +  15HC1  +  5HNO3->3SbCl5  +  5NO  t   +  10H2O 

SbCl5  +  8KOH  -»  K3SbO4  +  5KC1  +  4H2O 
2K3SbO4  +  3H2C2O4  +  5H2S-+3K2C2O4  +  Sb2S5  +  8H2O 

Sb2S5  +  8HCl-»2HSbCl4  +  2S  +  3H2S 

HSbCl4+2KClO3+ 3HCl-*SbCl5  +  2KC1  +  2C1O2  T   +  2H2O 
SbCU  +  2KI-»SbCl3  +  2KC1  +  I2 
I2  +  2Na2S2O3->Na2S4O6  +  2NaI 


NON-FERROUS  ALLOYS  315 

RAPID  VOLUMETRIC  ANALYSIS  OF  BEARING  METAL1 

Determination  of  Lead. — Weigh  1  g.  of  alloy  into  a  covered 
beaker  containing  2  to  5  g.  of  tartaric  acid  and  10  c.c.  of  water. 
Add,  while  stirring,  10  c.c.  of  7.5-normal  nitric  acid  (concentrated 
acid  with  an  equal  volume  of  water)  and  heat  below  60°  until  all 
of  the  alloy  has  dissolved.  While  heating  on  the  water  bath, 
add  2  or  3  drops  of  nitric  acid  if  it  seems  necessary.  A  clear 
solution  should  be  obtained.  Add,  while  stirring,  5  c.c.  of  con- 
centrated sulfuric  acid  diluted  with  an  equal  volume  of  water, 
and  evaporate  until  no  more  nitrous  fumes  are  evolved  but 
not  enough  to  cause  charring  of  the  tartaric  acid.  Cool,  dilute 
to  100  c.c.  and  filter  off  the  lead  sulfate,  washing  with  sulfuric 
acid  diluted  with  15  volumes  of  water.  Place  the  lead  sulfate 
precipitate  and  filter  in  a  flask,  add  10  c.c.  of  concentrated  hydro- 
chloric acid  and  boil  until  the  filter  is  well  disintegrated,  then 
add  15  c.c.  more  of  hydrochloric  acid,  25  c.c.  of  cold  water  and 
25  c.c.  of  strong  ammonia.  Introduce  a  few  drops  of  litmus 
solution,  add  enough  ammonia  to  make  alkaline  and  then  acetic 
acid  to  acid  reaction.  Heat  to  boiling  and  make  sure  that  all 
of  the  lead  sulfate  is  dissolved.  Dilute  to  200  c.c.  with  hot 
water  and  titrate  with  standard  ammonium  molybdate  solution. 
At  first  reserve  about  one-third  of  the  solution  and  add  the  molyb- 
date until  a  drop  of  the  solution  on  a  porcelain  "spot  plate" 
gives  a  brown  or  yellow  tinge  when  touched  with  a  drop  of  0.5 
per  cent  tannin  solution  in  water.  This  shows  that  the  end-point 
has  been  passed.  Add  about  half  of  the  reserved  solution  and 
again  titrate  until  the  end-point  is  passed  but  use  more  care  this 
time.  Finally  add  the  remaining  solution  to  the  contents  of  the 
flask  and  pour  the  solution  back  and  forth  from  flask  to  beaker 
several  times.  Finish  the  titration  by  adding  2  drops  at  a  time  of 
ammonium  molybdate.  Watch  the  burette  readings  toward  the 
last,  estimate  the  value  of  2  drops  of  the  solution,  and  deduct 
it  from  the  burette  reading  that  corresponds  to  the  first  appear- 
ance of  a  yellow  tinge. 

The  ammonium  molybdate  solution  may  be  prepared  by  dis- 
solving 4.74  g.  of  the  solid  in  1,000  c.c.  Standardize  against 
0.2-g.  portions  of  pure  lead  foil. 

1  This  method  of  analysis  is  not  recommended  for  precise  work  but'  an 
experienced  operator  can  get  good  results  with  it. 


316  CHEMICAL  ANALYSIS  OF  METALS 

Determination  of  Tin. — According  to  the  tin  content,  weigh 
out  0.2  to  1.0  g.  of  alloy  into  a  350-c.c.  Erlenmeyer  flask  and 
add  20  c.c.  of  concentrated  hydrochloric  acid.  When  most  of 
the  metal  has  dissolved  add  some  potassium  chlorate  in  small 
portions  until  all  the  alloy  has  dissolved.  Boil  off  the  chlorine, 
add  50  to  75  c.c.  of  concentrated  hydrochloric  acid,  according 
to  the  probable  antimony  content,  and  dilute  to  200  c.c. 

Prepare  a  metal  coil  from  a  heavy  sheet  of  nickel  (1.5  by  4  in.) 
and  place  it  in  the  flask,  leaving  a  narrow  strip  of  nickel  attached 
to  one  side  of  the  coil  to  reach  above  the  top  of  the  flask  when 
the  coil  rests  on  the  bottom.  Bend  this  strip  over  the  edge  of 
the  flask.  Boil  the  solution  gently  for  3  min.  to  reduce  any  iron 
present,  causing  the  yellow  color  to  turn  green.  Remove  from 
the  hot  plate  and  at  once  connect  with  a  carbon  dioxide  generator. 
Pass  carbon  dioxide  through  the  flask  until  the  solution  is  cold. 
Remove  the  stopper  from  the  flask  and  add  two  0.5-in.  cubes  of 
calcite  crystals.  Remove  the  nickel  coil  and  wash  it  with  cold, 
3-normal  hydrochloric  acid  while  withdrawing  it.  Add  a  little 
starch  solution  and  titrate  with  tenth-normal  iodine  solution. 
One  cubic  centimeter  of  tenth-normal  solution  =  0.005935  g.  of 
Sn. 

Determination  of  Antimony. — Weigh  1  g.  of  the  alloy  into  a 
300-c.c.  Kjeldahl  digestion  flask  and  heat  with  10  to  15  c.c.  of 
concentrated  sulfuric  acid  until  all  the  metal  is  dissolved  and  any 
sulfur  that  separates  is  volatilized.  About  7  c.c.  of  concentrated 
acid  should  remain  in  the  flask  so  that  a  hard  salt  cake  will  not 
form  on  cooling. 

Cool,  add  slowly  20  c.c.  of  water  and  20  c.c.  of  concentrated 
hydrochloric  acid.  Boil  until  certain  that  all  the  sulfur  dioxide 
has  been  expelled.  During  this  treatment  any  arsenic  will  be 
volatilized  as  trichloride  but  antimony  will  not. 

Cool  again,  add  water  to  a  volume  of  200  c.c.  and  adjust  the 
hydrochloric  acid  concentration  so  that  there  is  present  1  volume 
of  concentrated  acid  to  10  of  water  for  low  antimony  content 
and  1  to  5  for  high  antimony.  Titrate  the  cold  solution  with 
tenth-normal  potassium  permanganate  solution  until  1  drop  gives 
a  color  through  the  entire  solution.  The  color  soon  disappears. 
One  cubic  centimeter  of  tenth-normal  KMnO4  =  0.0060  g.  Sb. 


NON-FERROUS  ALLOYS  317 

Determination  of  Copper.  —  Dissolve  1  g.  of  alloy  in  45  c.c.  of 
concentrated  hydrochloric  acid  and  5  c.c.  of  concentrated  nitric 
acid.  Boil  down  to  15  or  20  c.c.  to  remove  all  free  chlorine. 
Wash  down  the  sides  of  the  flask  and  cover-glass  with  a  little 
6-normal  hydrochloric  acid  from  a  wash  bottle.  Dilute  to  75  c.c. 
and  add  5  g.  of  tartaric  acid  dissolved  in  20  c.c.  of  water.  Make 
the  solution  alkaline  with  ammonium  hydroxide  and  add  hydro- 
chloric acid  until  the  blue  color  of  copper-ammonia  ions  changes 
to  green,  showing  that  the  solution  is  slightly  acid.  If  necessary 
heat  to  dissolve  lead  chloride.  Add  2  c.c.  of  stannous  chloride 
solution  (225  g.  in  1,000  c.c.  of  6-normal  HC1)  and  0.5  g.  of 
potassium  thiocyanate.  Heat  for  a  few  minutes  and  filter  off 
the  white  precipitate  of  cuprous  thoicyanate.  Wash  with  hot 
water  until  the  excess  thiocyanate  is  removed. 

Place  the  filter  and  its  contents  in  a  250-c.c.  glass-stoppered 
bottle  and,  by  means  of  a  piece  of  moist  filter  paper,  transfer 
into  the  bottle  any  precipitate  that  adheres  to  the  beaker  or 
stirring-rod.  Add  5  c.c.  of  chloroform,  20  c.c.  of  water  and  30  c.c. 
of  concentrated  hydrochloric  acid.  Titrate  with  standard  potas- 
sium iodate  solution  until,  on  shaking,  no  blue  color  is  seen  in 
the  chloroform. 

The  iodine  is  formed  by  the  reaction: 

2CuSCN  +  3KI03  +  4HCl-+2CuSO4  +  IC1  +I2  +  2HCN  + 

H2O  +  3KC1 

but  disappears  as  soon  as  sufficient  potassium  iodate  has  been 
added 

2I2  +  KI03  +  6HC1->KC1  +  5IC1  +  3H2O 
The  entire  reaction  is  then: 


4CuSCN  +  7KI03  +  14  HC1^4CuSO4  +  7IC1  +4HCN  + 

+  7KC1  +  5H2O 

A  convenient  strength  for  the  standard  potassium  iodate  solu- 
tion is  one-fifth  gram-molecular-weight  per  liter.  Such  a  solu- 
tion is  obtained  by  dissolving  42.80  g.  of  pure  potassium  iodate 
in  water  and  diluting  to  exactly  1  liter  in  a  calibrated  flask. 
One  cubic  centimeter  of  such  a  solution  =  0.007265  g.  of  Cu. 


318  CHEMICAL  ANALYSIS  OF  METALS 

ARSENIC 

The  presence  of  a  small  quantity  of  arsenic  has  a  serious  effect 
upon  the  electrical  conductivity  of  copper.  The  chemist,  there- 
fore, is  often  called  upon  to  determine  the  arsenic  content  of 
copper  and  the  method  of  analysis  is  applicable  to  any  alloy. 

By  dissolving  in  hydrochloric  acid  in  the  presence  of  ferric  ions, 
the  arsenic  is  converted  into  arsenic  trichloride1  which  distils  off 
with  hydrochloric  acid.  The  distillate  can  be  collected  and,  after 
neutralizing,  the  arsenic  can  be  titrated  with  tenth-normal  iodine 
solution.  Since  hydrochloric  acid  often  contains  a  little  arsenic 
it  is  necessary  to  run  a  blank  test  using  all  the  details  of  manipu- 
lation as  in  the  actual  analysis. 

DETERMINATION  OF  ARSENIC  IN  A  COPPER  ALLOY 

Weigh  1  g.  of  the  alloy  into  a  distilling  flask  and  add  10  c.c. 
of  ferric  chloride  solution  (d.  1.43)  60  c.c.  of  concentrated  hydro- 
chloric acid,  20  c.c.  of  water  and  5  g.  of  solid  potassium  chloride. 
Connect  the  flask  with  a  condenser  and  heat  gently  until  the  metal 
is  all  in  solution.  Then  distil  until  only  a  little  liquid  remains 
in  the  flask,  catching  the  distillate  in  a  flask  surrounded  by  ice. 
Add  50  c.c.  more  of  hydrochloric  acid  and  repeat  the  distillation. 

To  the  cold  distillate  add  25  g.  of  solid  sodium  hydroxide  in 
small  pieces  and  finish  the  neutralization  of  the  solution  with 
sodium  carbonate,  being  careful  to  keep  the  solution  cold  and  to 
avoid  loss  by  effervescence.  Add  the  sodium  carbonate  until 
the  solution  is  no  longer  acid  to  litmus  then  add  1  g.  of  sodium 
bicarbonate  and  a  little  fresh  starch  solution.  Titrate  with 
0.02  normal  iodine  until  a  blue  color  is  obtained  One  cubic 
centimeter  of  0.02-normal  iodine  0.00075  g.  of  As. 

The  reactions  that  take  place  in  this  analysis  are  as  follows : 

Cu  -f  2Fe+++^Cu++  +  2Fe++ 
As  +  3Fe+++  +  3HCl^AsCl3  +  3Fe++  +  3H+ 
AsCl3  +  H2O  +  2Na2CO3-+NaH2AsO3  +  3NaCl  +  2CO2  T 

NaH2AsO3  +  I2  +  2NaHCO3-+NaH2AsO4  +  2NaI  + 
2CO2  t   +  H2O 

As  long  as  the  solution  is  saturated  with  CO2  there  is  no  danger  of 
NalO  being  formed  from  sodium  carbonate  and  iodine. 

1  Arsenic  chloride  boils  at  132°  and  freezes  at  — 18°.  It  distils  with  hydro- 
chloric acid  more  readily  than  stannic  chloride,  boiling  point  113.9°. 


NON-FERROUS  ALLOYS  319 

COPPER 

This  element  constitutes  the  principle  ingredient  of  most  of 
the  alloys  mentioned  in  this  chapter.  It  is  one  of  the  easiest 
metals  to  determine  quantitatively;  it  is  easily  deposited  electro- 
lytically,  forms  several  characteristic  insoluble  compounds  which 
can  be  weighed  with  accuracy,  can  be  titrated  volumetrically  in 
at  least  three  different  ways,  and  forms  highly  colored  ions, 
particularly  with  ammonia.  On  p.  146  a  rapid  and  accurate 
volumetric  method  was  described.  Chief  emphasis  will  be 
placed  here  upon  the  method  of  attacking  typical  copper  alloys, 
such  as  brass  and  bronze  and  three  procedures  for  determining 
the  element  electrolytically  and  another  well-known  volumetric 
method  will  be  described.  The  utility  of  the  method  must  be 
considered  as  well  as  the  accuracy;  the  electrolytic  and  volume- 
tric methods  for  determining  copper  are  easier  to  carry  out  and 
just  as  accurate  as  other  methods  which  might  be  mentioned, 
such  as  the  gravimetric  determination  as  cupric  oxide,  cuprous 
sulfide  or  cuprous  thiocyanate. 

Brass  is  an  alloy  of  copper  and  zinc  but  is  likely  to  contain 
small  quantities  of  other  elements  (cf.  p.  307).  If  a  clear 
solution  in  nitric  acid  is  obtained  which  shows  no  turbidity 
on  standing  for  some  time  in  a  warm  place,  it  may  be  assumed 
that  no  tin  is  present.  If  a  slight  turbidity  is  formed  it  may 
be  regarded  as  pure  metastannic  acid,  but  if  a  considerable 
precipitate  results,  the  alloy  is  to  be  regarded  as  a  bronze  and 
the  metastannic  acid  should  be  purified.  The  analysis  of  brass 
and  bronze  for  tin  will  be  considered  at  this  place  because  it  is 
advisable  to  remove  tin  before  determining  the  copper  and  lead 
and  small  quantities  of  lead  and  copper  are  often  found  in  the 
metastannic  acid.  Lead  will  be  discussed  because  it  is  easy  to 
determine  lead  and  copper  simultaneously. 

ANALYSIS  OF  BRASS  AND  BRONZE1 

Dissolving  the  Alloy.— Weigh  1  g.  of  alloy  into  a  beaker  of 
about  150-c.c.  capacity.  Cover  the  beaker  with  a  watch-glass 
and  add  10  c.c.  of  strong  nitric  acid.  When  the  action  has 

1  The  methods  given  in  this  chapter  are  based  for  the  most  part  upon  the 
procedures  recommended  by  the  American  Society  for  Testing  Materials. 
The  directions  have  been  modified  somewhat. 


320  CHEMICAL  ANALYSIS  OF  METALS 

ceased,  wash  down  the  sides  of  the  beaker  and  the  cover  glass, 
raise  the  latter  by  means  of  a  glass  triangle  and  evaporate  the 
solution  to  dryness  without  boiling  the  solution  or  overheating  the 
residue.  Moisten  the  dry  residue  with  2  c.c.  of  6-normal  nitric 
acid  and  digest  a  short  time  near  the  edge  of  a  hot  plate.  Add  50 
c.c.  of  hot  water,  heat  to  boiling  and  keep  the  solution  hot  but  not 
boiling  for  1  hr.  If  there  is  any  residue1  filter  the  hot  solution 
through  a  7-cm.  filter,  containing  some  macerated  filter-paper 
pulp,  into  an  electrolyzing  beaker  of  about  150-c.c.  capacity  and 
with  relatively  high  sides  and  narrow  cross-section. 

Wash  the  precipitate  with  small  portions  of  hot  water  until 
the  washings  are  neutral  to  litmus.  Carefully  examine  the 
filtrate  and  refilter  if  necessary.  The  first  and  last  portions  of 
filtrate  are  the  most  likely  to  show  turbidity  and  for  this  reason 
it  is  best  to  collect  the  filtrate  in  a  small  beaker  and  transfer  it  to 
the  electrolyzing  beaker  in  portions  found  to  be  clear;  in  this  way 
it  will  never  be  necessary  to  refilter  the  entire  solution. 

1  The  evaporation  and  digestion  with  nitric  acid  are  necessary  to  remove 
the  last  traces  of  tin  from  the  solution.  Tin  dissolves  in  dilute  nitric  acid 
to  form  stannous  nitrate  but  the  stannous  ions  are  easily  oxidized  to  the 
stannic  condition  and  a  gelatinous  precipitate  forms  as  a  result  of  hydrolysis. 
The  stannic  acid  remains  in  colloidal  solution  at  first  but  tends  to  change 
into  the  hydrogele.  The  evaporation  with  nitric  acid  also  causes  precipi- 
tation of  any  silicon  as  silicic  acid  and  it  is  sometimes  doubtful  whether  a 
slight  precipitate  is  silicic  acid  or  metastannic  acid;  in  the  former  case 
it  may  arise  from  silicon  in  the  alloy  or  from  the  action  of  acid  upon  glass. 
Silicic  acid  can  be  distinguished  from  metastannic  acid  by  heating  with 
sulfuric  and  hydrofluoric  acids  in  platinum.  In  alloy  analysis,  the  use  of 
platinum  crucible  is  avoided  as  much  as  possible  for  heating  precipitates, 
because  a  relatively  small  quantity  of  copper,  lead  or  other  reducible  metal 
when  ignited  with  filter  paper  is  likely  to  spoil  the  crucible. 

The  last  traces  of  tin  are  hard  to  precipitate  as  metastannic  acid.  Cer- 
tain substances,  particularly  chlorides,  exert  a  so-called  peptonizing  effect 
and  convert  the  hydrogele  to  hydrosole. 

The  literature  is  full  of  conflicting  statements  concerning  the  purity  of 
metastannic  acid  as  obtained  in  alloy  analysis.  It  is  perfectly  true  that 
fairly  pure  precipitates  are  often  obtained  and  that  it  is  not  always  necessary 
to  purify  the  precipitate.  All  colloids,  however,  show  more  or  less  ten- 
dency to  adsorb  certain  substances  in  solution  and  the  extent  of  the  adsorp- 
tion is  greater  in  more  concentrated  solutions  and  the  adsorption  increases 
on  standing.  Arsenic  acid  and  phosphoric  acid  are  adsorbed  to  a  marked 
degree  by  metastannic  acid  and  iron,  titanium,  copper,  lead,  etc.  are  often 
found  in  the  precipitate. 


NON-FERROUS  ALLOYS  321 

Determination  of  Tin. — Transfer  the  precipitated  metastannic 
acid  and  filter  paper  to  a  weighed  porcelain  crucible.  Heat  care- 
fully with  a  small  flame  at  the  mouth  of  the  crucible  until  the 
paper  is  dry  then  place  the  flame  at  the  base  of  the  inclined 
crucible  and  heat  with  a  low  flame  until  the  paper  is  all  consumed 
without  taking  fire.  Ignite  strongly  for  10  min.,  cool  in  the  air 
until  below  100°  and  then  in  a  desiccator.  When  cold  it  is  ready 
to  weigh. 

If  the  weight  of  stannic  oxide  corresponds  to  less  than  2  per 
cent  tin  in  the  sample  it  may  be  regarded  as  pure,  containing 
78.80  per  cent  Sn.  If  more  than  2  per  cent  of  tin  is  present,  the 
stannic  oxide  should  be  purified. 

To  purify  the  precipitate,  add  10  times  as  much  of  a  mixture  of 
equal  parts  sodium  carbonate  and  sulfur.  Mix  well,  cover  the  cru- 
cible and  heat  with  a  low  flame  until  the  flame  of  burning  sulfur  is 
no  longer  visible  around  the  edges  of  the  cover.  Cool  and  leach 
out  the  soluble  sodium  salts  with  hot  water.  The  aqueous  extract 
contains  the  tin  as  sodium  thiostannate,  together  with  sodium 
thioarsenate  and  sodium  thioantimonate  if  arsenic  and  anti- 
mony are  present.  Traces  of  copper  sulfide,  and  other  sulfides, 
are  dissolved  by  the  excess  of  polysulfide  formed  during  the  fusion. 
Add  a  little  sodium  sulfite  or  thiosulfate  until  the  deep  brown 
color  of  the  solution  disappears  and  heat  to  coagulate  the  insol- 
uble sulfides.  Filter  and  wash  thoroughly  with  hot  water,  using 
hydrogen  sulfide  water  toward  the  last.  Ignite  the  precipitate 
carefully  in  a  weighed  porcelain  crucible  and  dissolve  the  oxide 
residue  in  a  few  drops  of  nitric  acid.  Add  the  resulting  solution 
to  the  original  nitric  acid  solution  of  the  alloy.  In  case  no  phos- 
phorus is  present,  the  weight  of  these  last  oxides  subtracted 
from  the  weight  of  the  impure  stannic  oxide  will  give  the  weight 
of  pure  stannic  oxide.  This  weight,  however,  may  be  determined 
by  direct  analysis  as  follows: 

Add  hydrochloric  acid  to  the  aqueous  extract  of  the  sodium 
carbonate  fusion  until  slightly  acid,  saturate  with  hydrogen 
sulfide,  heat  to  boiling  and  filter.  Wash  the  precipitate  of 
stannic  sulfide  with  hot  water  until  free  from  chloride  and  ignite 
carefully  in  a  weighed  porcelain  crucible.  Do  not  allow  the 
paper  or  sulfur  to  take  fire  as  there  is  danger  of  losing  some  stan- 
nic sulfide  by  volatilization  or  of  forming  some  stannic  sulfate; 
21 


322  CHEMICAL  ANALYSIS  OF  METALS 

the  former  error  causes  low  results  and  high  values  result  from 
the  latter  error.  Finally  heat  over  the  Meker  burner  and  weigh 
as  stannic  oxide,  SnO2. 

The  chemical  reactions  that  take  place  in  the  analysis  for  tin 
may  be  expressed  by  the  following  equations : 

3Sn  +  4H+  +  4NO8~  +  H2O^3H2SnO3  +  4NO  T 
2SnO2  +  9S  +  2Na2CO3^2Na2SnS3  +  3SO2  +  2CO  T 
2CuO  +  3S^2CuS  +  SO2  T 
Na2SnS3  +  2HCl-»2NaCl  +  H2S  |    +  SnS2 
SnS2  +  2O2-»SnO2  +  2SO2  T 

Determination  of  Tin. — Alternate  Method. — The  American 
Society  for  Testing  Materials  recommends  the  following  pro- 
cedure: Dissolve  2  g.  of  alloy  in  10  c.c.  of  concentrated  hydro- 
chloric acid  and  5  c.c.  of  concentrated  nitric  acid.  Dilute  the 
solution  to  75  c.c.,  add  a  slight  excess  of  ammonium  hydroxide, 
filter,  wash  the  precipitate  with  dilute  ammonium  hydroxide 
and  discard  the  filtrate.  Dissolve  the  precipitate  in  hot  dilute" 
hydrochloric  acid,  dilute  to  75  c.c.  -and  again  precipitate  with 
ammonium  hydroxide  as  before.  Dissolve  the  precipitate  in 
hot,  dilute  sulfuric  acid  and  for  the  third  time  add  ammonium 
hydroxide  but  stop  when  the  solution  is  barely  acid.  Allow  the 
solution  to  stand  and  if  any  lead  sulfate  forms,  filter  it  off. 
Saturate  the  solution  with  hydrogen  sulfide,  heat  to  boiling, 
filter  and  wash  the  stannic  sulfide  precipitate  with  ammoniurn 
nitrate  solution.  Dry,  ignite  very  carefully  in  a  weighed  porce- 
lain crucible,  and  finally  heat  strongly  and  weigh,  when  the 
crucible  is  cold,  as  stannic  oxide,  SnO2. 

The  reactions  that  take  place  in  this  method  of  analysis  may  be 
expressed  as  follows: 

3Sn  +  12HC1  +  4HN03-^3SnCl4  +  8H2O  +  4NO  T 
3Cu  +  6HC1  +  2HNO3-»3CuCl2  +  4H2O  +  2NO  T 
SnCU  +  4NH4OH-+Sn(OH)4  +  4NH4C1 
Cu++  +  4NH4OH-*Cu(NH3)4++  +  4H2O 
Sn(OH)4  +  2H2SO4-^Sn(SO4)2  +  4H2O 
Sn(S04)2  +  2H2S-»SnS2  +  H2S04 
SnS2  +  3O2-*SnO2  +  2SO2 

Method  A.    Determination  of  Lead  and  Copper. — This  method 
depends  upon  the  simultaneous  deposition  of  dioxide  upon  the 


NON-FERROUS  ALLOYS  323 

anode  and  metallic  copper  upon  the  cathode  by  the  electrolysis 
of  a  stirred  nitric  acid  solution,  obtained  as  described  above. 

Electrodes. — The  cathode  is  made  preferably  of  platinum 
gauze  with  about  400  meshes  per  square  centimeter  or  45  wires  to 
the  linear  inch.  It  should  be  stiffened  at  the  top  and  bottom  by 
doubling  the  gauze  or  by  welding  it  to  a  narrow  band  of  platinum. 
The  gauze  should  be  made  into  a  continuous  cylinder  about 
30  mm.  in  diameter  and  40  mm.  tall.  The  stem  should  be 
made  of  1.14  or  1.29-mm.  wire  and  welded  to  the  cylinder  from 
top  to  bottom.  Instead  of  the  gauze  electrode,  any  other  of 
the  well-known  shapes  of  electrodes  made  of  sheet  platinum 
may  be  used  but  gauze  electrodes  are  preferred  because  they 
permit  greater  diffusion  of  the  electrolyte  and  there  is  less  danger 
of  obtaining  spongy  deposits. 

The  anode  may  be  of  the  spiral  type  when  less  than  0.2  per 
cent  of  lead  is  present  but  a  gauze  electrode,  about  12  mm.  in 
diameter,  is  better.  In  brass  analysis  the  anode  should  fit  inside 
the  cathode  so  that  it  can  be  rotated  without  danger  of  touching. 
In  bronze  analysis  it  is  well  to  make  the  anode  larger  than  the 
cathode  because  the  lead  dioxide  does  not  adhere  as  well  to  the 
electrode  as  the  copper  does  and  for  this  reason  the  anode  should 
not  be  rotated  when  the  lead  content  is  more  than  a  few  tenths 
of  one  per  cent.  In  bronze  analysis,  therefore,  it  is  better  to 
rotate  the  cathode,  if  it  is  desired  to  stir  the  electrolyte  so  that 
considerable  current  can  be  used,1  without  the  formation  of 
spongy  copper.  This  can  be  accomplished  satisfactorily,  as 
suggested  by  Gooch,  by  using  a  platinum  crucible  as  cathode. 
The  crucible  is  fastened  to  the  negatively  charged  rotating  shaft 
of  the  stirrer  by  means  of  a  rubber  stopper  and  electrical  connec- 
tion made  by  means  of  a  wire  pressing  against  the  crucible  and 
attached  to  the  shaft.  Deposits  adhere  better  to  sand-blasted 
electrodes  than  to  polished  ones. 

Procedure. — Use  as  electrolyzing  beaker  one  that  is  just  large 
enough  to  hold  the  electrodes  conveniently,  so  that  not  over 
100  c.c.  of  solution  suffice  to  wet  at  least  three-quarters  of  the 
electrode  surface.  Before  placing  the  weighed  electrodes  in 
the  beaker,  make  all  the  electrical  connections  and  be  sure  that 

1  With  stationary  plate  electrodes,  a  current  of  about  0.2  ampere  will 
give  satisfactory  results  in  about  20  hr  . 


324  CHEMICAL  ANALYSIS  OF  METALS 

the  electrode  to  be  rotated  is  properly  centered.  Adjust  the 
beaker  support  so  that  the  stationary  electrode  touches  the 
bottom  of  the  beaker.  The  electrolyte  should  not  exceed  100 
c.c.  in  volume  and  is  obtained  as  described  on  page  320. 

With  the  current  turned  off,  and  the  electrodes  and  beaker  in 
place,  start  the  stirrer  to  make  sure  that  there  will  be  no  spattering 
when  it  revolves  at  a  rate  of  600  to  900  r.p.m.  Turn  on  about 
3  amperes  of  current  and  note  the  time.  When  the  solution 
has  become  colorless,  add  about  0.1  g.  of  urea  and,  if  there  is 
marked  effervescence  produced,  carefully  add  enough  more  urea 
to  decompose  all  the  nitrous  acid,  which  prevents  complete 
deposition  of  copper.  Reduce  the  current  to  about  1  ampere 
and  electrolyze  10  min.  longer.  Then  wash  down  the  sides  of 
the  beaker  and  note  whether  there  is  any  further  deposition  of 
copper  upon  the  freshly  wetted  surface  after  5  min. 

When  convinced  that  all  the  copper  has  been  deposited,  start 
removing  the  beaker,  without  turning  off  the  current,  and  wash 
both  electrodes  while  withdrawing  the  beaker.  Then  turn  off 
the  current  and  promptly  rinse  the  electrodes  with  water  and 
give  them  two  baths  with  95  per  cent  alcohol.  Dry  the  anode  at 
180  to  210°  for  30  min.  and  weigh  as  PbO2.  Dry  the  cathode  at 
110°,  watching  it  as  it  dries,  and  remove  as  soon  as  no  more 
dampness  is  visible.1  Cool  and  weigh. 

Test  the  solution  for  copper  by  making  it  ammoniacal.  If  any 
sign  of  blue  color  is  obtained,  acidify  with  dilute  sulfuric  acid  and 
electrolyze  some  more  with  clean  electrodes. 

NOTES. — The  results  of  the  lead  determination  are  likely  to  be 
a  little  high  as  the  deposit  tenaciousty  retains  a  little  moisture. 
The  error  from  this  source  can  be  disregarded  in  the  analysis 
of  brass  and  bronze. 

The  reactions  that  take  place  in  the  determination  of  lead  and 
copper  in  brass  and  bronze  may  be  expressed  as  follows,  using 
©  to  represent  a' unit  charge  of  negative  electricity: 

3Cu  +  2NO3~  +  8H+  -*3Cu++  +  2NO  T    +  4H2O 
3Pb  +  2N03~  +  8H+  -*3Pb++  +  2NO  T    +  4H2O 

Cu++  +  2©  ->  Cu 
Pb++  +  2H20  -  2©  -»  PbO2  +  4H+ 

1  The  excess  of  alcohol  may  be  shaken  off  and  the  electrode  dried  by  burn- 
ing the  alcohol  that  remains.  Unless  the  electrode  is  kept  in  motion  this 
will  cause  oxidation  of  a  little  copper  and  a  black  stain  of  oxide  will  result. 


NON-FERROUS  ALLOYS  325 

As  explained  on  page  265,  96,500  coulombs  =  96,500  ampere- 
seconds  are  required  to  deposit  31.8  g.  of  copper,  or  1  ampere- 
second  will  deposit  0.328  mg.  copper.  To  precipitate  0.7  g.  of 
copper,  which  corresponds  to  the  copper  content  of  1  g.  of  good 
cartridge  brass,  a  current  of  3  amperes  would  require  about  12 
min.  if  the  current  is  utilized  entirely  for  depositing  copper. 

As  mentioned  on  p.  266,  the  copper  is  harder  to  deposit 
as  the  concentration  falls  and  stirring  helps  to  bring  copper  ions 
into  contact  with  the  cathode.  With  gauze  electrodes  in  a  small 
beaker,  there  is  more  diffusion  throughout  the  electrolyte  than 
when  the  electrodes  are  solid  plates  in  a  dilute  solution  and  the 
passage  of  a  fairly  strong  current  causes  heating  which  starts 
convection  currents.  It  is  inevitable,  however,  that  the  dis- 
charge potential  of  some  other  ion  in  solution  will  be  reached 
before  the  last  trace  of  copper  is  deposited.  Next  to  copper 
the  two  ions  most  likely  to  be  discharged  at  the  cathode  in  an 
acid  solution  are  hydrogen  ions  and  nitrate  ions: 

2H+  +  2©  ->  H  (1) 

NO3~  +  10H+  +  8©  -»  NH4+  +  3H2O  (2) 

N03~  +  2H+  +  2©  ->  N02~  +  H2O  (3) 

The  discharge  of  hydrogen  ions  together  with  copper  is  the  cause 
of  spongy  deposits.  If  the  reduction  of  the  nitrate  ion  takes 
place  to  form  an  appreciable  quantity  of  nitrous  acid,  the  further 
deposition  of  copper  is  prevented  and  in  many  cases  the  copper 
begins  to  dissolve.  The  purpose  of  adding  urea  is  to  decompose 
nitrous  acid1  but  under  the  conditions  recommended  there  is  not 
much  formed  unless  too  much  current  is  used.  The  reduction 
of  the  nitrate  ion  may  cause  lessening  of  the  acidity  as  equation 
(2)  shows;2  eventually  the  solution  becomes  neutral  and  then 
zinc  will  precipitate.  Many  chemists  prefer  to  electrolyze 
sulfuric  acid  solutions  because  there  is  not  this  danger  of  the 
solution  becoming  neutral  if  nitrate  ions  are  absent  but,  on  the 
other  hand,  ammonium  nitrate  is  often  added  to  prevent  the 
formation  of  spongy  copper.  If  the  nitric  acid  is  absolutely 


+2HNO2—  >2N2      +  CO2       +  3H2O. 

2  Equations  (1)  and  (3)  do  not  cause  loss  of  acidity  because  H+  ions 
are  being  formed  at  the  anode  in  equal  amount  to  those  removed  at  the 
cathode. 

2H20  -  40-»4H+  +O2. 


326  CHEMICAL  ANALYSIS  OF  METALS 

free  from  nitrous  acid,  it  does  not  dissolve  copper.  A  little 
nitrous  acid  is  likely  to  be  present  and  when  the  reaction  between 
copper  and  nitrous  acid  takes  place,  more  nitrous  acid  is  formed 
so  that  it  is  not  safe  to  leave  the  deposit  in  contact  with  the 
solution  when  the  current  is  turned  off. 


2NO2~  +  Cu  +  4H+^Cu++  +  2NO  +  2H2O 
2NO  +  NO3~  +  H2O^3N02-  +  2H+ 


Method    B.     Electrolysis    with    Stationary    Electrolyte.  —  In 

this  method,  which  is  advocated  by  the  American  Society  for 
Testing  Materials,  the  solution  is  kept  hot  which  serves  to  hasten 
the  electrolysis,  partly  by  changing  the  resistance  of  the  elec- 
trolyte and  partly  by  causing  diffusion  currents  to  stir  up  the 
solution.  In  the  hot  solution  there  is  also  less  danger  of  a  little 
manganese  dioxide  deposit  forming  on  the  anode.  Use  as 
electrodes  a  pair  of  sand-blasted,  gauze  electrodes  of  the  size 
recommended  on  page  323.  To  the  solution  obtained  as  de- 
scribed on  page  320,  add  enough  nitric  acid  to  make  it  contain 
10  per  cent  by  weight.  This  is  «asy  to  estimate  because  the 
acid  in  1  c.c.  of  15-normal  nitric  acid  (d.  1.42)  weighs  nearly 
1  g.  Heat  the  solution  to  boiling  and  boil  very  gently  for  1  min. 
to  remove  nitrous  acid.  Then  electrolyze  the  hot  solution  at  a 
volume  of  about  100  c.c.  with  a  current  of  3  to  5  amperes  and 
approximately  10  volts  between  the  electrodes.  After  about 
45  min.  the  lead  will  have  been  completely  deposited  and  the 
concentration  of  the  nitric  acid  will  have  been  reduced  materially 
by  cathodic  reduction,  as  explained  under  Method  A.  The 
presence  of  nitric  acid  favors  the  deposition  of  the  lead  as  dioxide 
upon  the  anode  but  too  much  nitric  acid  was  added  to  permit 
the  complete  deposition  of  the  copper  in  this  time.  Add  3  c.c.  of 
concentrated  sulfuric  acid  and  electrolyze  until  the  solution  is 
colorless.  Wash  down  the  cover  glass,  electrodes  and  sides  of  the 
beaker  and  see  if  any  more  copper  is  deposited.  When  the 
electrolysis  is  finished  remove  the  electrodes  as  described  in 
Method  A. 

NOTES.  —  Considerable  phosphoric,  arsenic,  telluric  and  selenic 
acids  will  prevent  the  deposition  of  lead  as  dioxide  but  there  is 
never  enough  of  these  elements  found  in  brass  or  bronze  to  cause 
errors  of  this  nature. 


NON-FERROUS  ALLOYS  327 

The  deposited  copper  is  dissolved  off  the  electrode  without 
difficulty  by  warming  with  3-normal  nitric  acid.  A  slight  deposit 
of  lead  dioxide  will  dissolve  in  this  acid  but  it  dissolves  more 
rapidly  if  a  little  hydrogen  peroxide,  or  oxalic  acid,  is  added  to 
the  nitric  acid  solution. 

Manganese  and  bismuth  are  the  only  other  common  metals 
likely  to  deposit  upon  the  anode.  To  test  the  anode  deposit  for 
bismuth  and  manganese,  dissolve  it  in  nitric  acid  with  a  few  drops 
of  hydrogen  peroxide.  Add  2  c.c.  of  concentrated  sulfuric  acid 
and  evaporate  to  fumes.  Cool,  pour  into  25  c.c.  of  cold  water 
and  allow  the  lead  sulfate  precipitate  to  settle.  Filter  and  apply 
the  usual  qualitative  tests  for  bismuth  and  manganese. 

Method  C.  Removal  of  Lead  as  Sulfate  and  Determination 
of  the  Copper  by  Electrolysis  or  by  the  Iodide  Method. — Dissolve 
5  g.  of  the  alloy  in  25  c.c.  of  concentrated  nitric  acid  and  precipi- 
tate any  tin  as  metastannic  acid  by  evaporating  to  dryness. 
Add  16  c.c.  of  concentrated  nitric  acid  to  the  residue  and  digest 
a  short  time  at  90°.  Add  85  c.c.  of  hot  water  and  boil  gently  for 
a  few  minutes.  Filter  off  the  metastannic  acid  as  described  on 
page  320  and  after  adding  10  c.c.  of  concentrated  sulfuric  acid 
evaporate  the  nitrate  till  copious  fumes  are  evolved.  Cool,  pour 
into  50  c.c.  of  cold  water,  boil  to  dissolve  all  the  copper  sulfate, 
cool  and  allow  the  lead  sulfate  to  settle  at  least  5  hr. 

Filter  off  the  precipitate  into  a  properly  prepared  and  weighed 
Gooch  crucible1  and  wash  with  5-c.c.  portions  of  5  per  cent 
sulfuric  acid.  Remove  the  nitrate  and  finish  washing  with  a 
little  50  per  cent  alcohol.  Place  the  Gooch  crucible  in  a  larger 
porcelain  crucible,  dry  carefully  and  finally  heat  5  min.  with  the 
full  heat  of  a  Tirrill  burner.  Cool  and  weigh  as  lead  sulfate 
containing  68.29  per  cent  lead. 

Or,  instead  of  determining  the  lead  as  sulfate,  it  may  be 
collected  upon  a  paper  filter  and  dissolved  in  a  hot  ammonium 
acetate  solution  (1  vol.  concentrated  ammonia:  1  vol.  water: 
enough  80  per  cent  acetic  acid  to  make  the  solution  barely  acid) . 
Rinse  the  precipitate  into  a  small  beaker  by  a  stream  of  hot  water 
from  the  wash  bottle  and  dissolve  the  part  that  adheres  to  the 
filter  by  pouring  small  portions  of  the  ammonium  acetate  solution 
through  the  filter,  followed  by  a  little  hot  water,  until  a  portion  of 

1  It  must  have  been  heated  as  in  the  analysis. 


328  CHEMICAL  ANALYSIS  OF  METALS 

the  filtrate  gives  no  blackening  with  ammonium  sulfide  solution. 
It  is  well  to  use  as  little  ammonium  acetate  as  possible  because  it 
exerts  a  slight  solvent  effect  upon  the  lead  chromate.  Dilute  the 
solution  to  50  c.c.  and  add  just  enough  saturated  potassium 
dichromate  solution  to  color  it.  Heat  to  coagulate  the  precipi- 
tate, filter  into  a  properly  prepared  Gooch  crucible,  wash  with 
water  and  dilute  alcohol,  dry  at  110°  for  an  hour  and  weigh. 
Calculate  the  lead  on  the  assumption  that  the  precipitate  contains 
63.75  per  cent  lead. 

A  precipitate  of  lead  sulfate  which  can  hardly  be  seen  will 
give  a  characteristic  lead  chromate  precipitate. 

Transfer  the  sulfuric  acid  solution  from  which  the  lead 
has  been  removed,  to  a  500-c.c.  calibrated  flask.  Make  up 
to  the  mark  at  room  temperature,  mix  thoroughly  and  pipette 
off  50  c.c.  of  the  solution  for  the  determination  of  copper, 
zinc,  etc. 

The  copper  may  be  determined  in  either  of  the  following  ways : 
(1)  Add  1  g.  of  solid  ammonium  nitrate  and  electrolyze  as  in 
Method  A.  (2)  Titrate  with  sodium  thiosulfate  as  described 
below : 

lodometric  Determination  of  Copper  in  Alloys.  This  method 
can  be  applied  directly  to  the  analysis  of  such  metals  as  brass, 
bronze  and  German  silver  and  is  accurate. 

Procedure. — Dissolve  0.5  g.  of  alloy  in  a  250-c.c.  flask  with 
about  10  c.c.  of  aqua  regia.  Boil  off  the  excess  acid  by  heating 
over  a  low  flame  but  keeping  the  flask  in  constant  motion. 
Dilute  with  water  to  about  50  c.c.  and  add  sodium  carbonate 
solution  until  nearly  neutral  and  a  blue  precipitate  of  basic 
copper  carbonate  is  obtained.  Dissolve  the  precipitate  in  a 
slight  excess  of  acetic  acid  and  boil  to  expel  carbonic  acid.  If  a 
precipitate  of  basic  ferric  acetate  forms,  remove  it  by  filtration 
and  wash  with  hot  water.  Cool  to  room  temperature,  add  3  g. 
of  solid  potassium  iodide.  Shake  and  after  2  min.  titrate  with 
sodium  thiosulfate  solution  until  the  mixture  is  faintly  yellow. 
Then  add  a  little  fresh  starch  solution  and  titrate  until  the  deep 
blue  color  disappears  and  a  pink  precipitate  of  cuprous  iodide 
remains  (cf.  p.  147). 

One  cubic  centimeter  of  tenth-normal  sodium  thiosulfate 
solution  =  0.00636  g.  Cu. 


NON-FERROUS  ALLOYS  329 

IRON 

Proceed  as  in  the  analysis  for  tin,  page  322.  Take  the  nitrate 
from  the  tin  sulfide  precipitate,  boil  off  hydrogen  sulfide  and 
oxidize  by  adding  a  little  bromine  water.  Add  a  slight  excess 
of  ammonium  hydroxide,  heat  to  boiling  and  filter.  The  precipi- 
tate will  contain  any  iron  as  hydroxide  and  possibly  other 
hydroxides  which  will  not  interfere  with  the  iron  determination. 
Dissolve  the  precipitate  on  the  filter  with  a  little  hot,  dilute 
hydrochloric  acid.  A  good  way  is  to  first  moisten  the  precipitate 
with  hot  water,  pour  about  2  c.c.  of  3-normal  hydrochloric  acid 
upon  it,  and  wash  down  with  a  stream  of  hot  water,  catching  the 
filtrate  in  a  small  beaker.  Repeat  the  treatment  until  the  ferric 
hydroxide  is  all  dissolved  but  do  not  use  more  than  10  c.c.  of 
6-normal  hydrochloric  acid.  There  should  be  no  yellow  stain  of 
ferric  chloride  remaining  on  the  filter.  Heat  the  solution  to 
boiling,  reduce  with  stannous  chloride  and  titrate  as  described 
on  page  232. 

LEAD 

The  analysis  of  typical  lead  alloys  has  been  discussed  on  page 
312  and  on  page  322. 

MANGANESE 

The  principles  upon  which  various  methods  of  determining 
manganese  in  alloys  depend  have  been  explained  in  Chaps.  Ill  and 
XXI.  The  following  procedures  are  suitable  for  the  analysis  of 
commercial  non-ferrous  manganese  alloys  in  which  the  manganese 
content  is  low. 

Persulfate  Method. — Dissolve  1  g.  of  alloy,  or  proportionately 
less  if  more  than  0.15  per  cent  of  manganese  is  present,  in  a  mix- 
ture of  5  c.c.  concentrated  sulfuric  acid,  2  c.c.  concentrated  nitric 
acid  and  17  c.c.  water.  Heat  until  the  alloy  is  dissolved  and  expel 
oxides  of  nitrogen.  Add  2  c.c.  of  tenth-normal  silver  nitrate 
solution  and  20  c.c.  of  6  per  cent  ammonium  persulfate  solution. 
Let  the  solution  heat  on  the  water  bath  until  a  good  permanganate 
color  results  and  no  gas  bubbles  are  seen  to  rise  when  the  solution 
in  the  flask  is  given  a  whirling  motion.  Cool  to  below  25°,  add 
50  c.c.  of  cold  water  and  titrate  with  approximately  0.06-normal 
sodium  arsenite  solution. 


330  CHEMICAL  ANALYSIS  OF  METALS 

Prepare  the  sodium  arsenite  solution  by  dissolving  4.3  g.of 
arsenious  oxide  with  10  g.  sodium  carbonate  and  30  c.c.  of  water. 
Filter  if  necessary  and  dilute  to  2000  c.c.  with  water.  One  cubic 
centimeter  of  this  solution  will  equal  approximately  0.0005  g. 
of  manganese. 

Standardize  the  sodium  arsenite  solution  against  pure  manga- 
nous  sulfate  crystals  obtained  by  drying  the  pure  crystals  at 
about  200°;  the  anhydrous  salt  contains  36.38  per  cent  Mn. 
Weigh  out  about  2  g.  of  the  manganous  salt  into  a  100- c.c.  cali- 
brated flask,  dissolve  in  a  little  water,  make  up  to  the  mark  and 
mix  thoroughly  by  pouring  back  and  forth  into  a  dry  beaker. 
Withdraw  10-c.c.  portions,  by  burette  or  pipette,  for  the  standard- 
ization and  proceed  exactly  as  in  the  analysis  of  the  alloy. 

Bismuthate  Method. — Dissolve  1.5  g.  of  alloy  in  50  c.c.  of  25 
per  cent  nitric  acid  (cf.  p.  50  and  p.  286).  Without  filtering, 
add  about  0.5  g.  of  bismuthate  and  heat  until  the  purple  color  of 
permanganate  disappears.  If  a  precipitate  of  manganese  dioxide 
is  obtained,  add  a  little  pure  ferrous  salt  to  dissolve  it  and  boil 
until  oxides  of  nitrogen  are  expelled.  Cool  to  at  least  20°  and 
add  a  slight  excess  of  sodium  bismuthate.  Filter  as  described 
on  page  52  and  titrate  the  manganese  as  described  there. 

NICKEL 

Dissolve  not  more  than  0.5  g.  of  drillings  in  10  o.c.  of  6-normal 
nitric  acid.  Filter  if  necessary.  Add  40  c.c.  of  water,  1  g.  of 
tartaric  acid  and  ammonia  until  a  deep  blue  color  of  copper- 
ammonia  ions  is  obtained.  Heat  to  about  50°,  add  an  excess  of 
1  per  cent  dimethylglyoxime  solution  and  finish  the  analysis 
as  described  on  p.  177. 

PHOSPHORUS 

Dissolve  1  g.  of  alloy  in  10  c.c.  of  concentrated  nitric  acid  in  a 
300-c.c.  casserole.  Add  20  c.c.  of  concentrated  hydrochloric 
acid  and  evaporate  to  dryness.  Moisten  the  residue  with 
hydrochloric  acid  and  add  3  c.c.  of  ferric  chloride  solution  (100  g. 
FeCl3  in  100  c.c.  water).  Dilute  to  about  200  c.c.,  add  ammon- 


NON-FERROUS  ALLOYS  331 

ium  hydroxide  until  the  basic  copper  salt  is  all  dissolved  and  then 
boil.  Allow  the  precipitate  of  ferric  hydroxide  and  phosphate 
(and  arsenate  if  arsenic  is  present)  to  settle,  filter  and  wash  with 
dilute  ammonia  and  water.  Dissolve  the  precipitate  in  hot, 
dilute  hydrochloric  acid,  dilute  to  200  c.c.  and  add  ammonia  until 
the  precipitate  that  forms  where  the  ammonia  comes  in  contact 
with  the  solution  dissolves  very  slowly  and  saturate  with  hydro- 
gen sulfide.  Heat  to  coagulate  the  precipitate,  filter  and  reject 
it.  Boil  the  solution  to  expel  hydrogen  sulfide,  add  concentrated 
nitric  acid  until  the  iron  is  all  oxidized  and  again  precipitate  with 
ammonia,  washing  as  before.  Dissolve  this  precipitate  in  6- 
normal  nitric  acid  and  receive  the  filtrate  in  a  300-c.c.  Erlenmeyer 
flask.  Add  ammonia  until  the  iron  is  all  precipitated  and  then 
just  enough  concentrated  nitric  acid  to  clear  up  the  solution. 
Heat  to  80°,  and  add  40  c.c.  of  ammonium  molybdate  solution. 
Allow  the  solution  to  stand  1  min.,  shake  for  3  min.  and  finish 
the  analysis  as  in  the  analysis  of  iron  and  steel.  (See  Chap.  IV.) 

TIN 
See  pp.  321  and  322. 

ZINC 

The  zinc  content  of  brass  and  bronze  is  often  determined  "by 
difference/'  i.e.  by  subtracting  all  of  the  other  values  obtained 
from  100  per  cent.  This  is  justifiable  in  many  cases  of  com- 
mercial testing  but  the  practice  is  a  dangerous  one.  If  any  error 
has  been  made  in  the  previous  work,  it  may  escape  detection. 

In  commercial  work  the  volumetric  method  depending  upon 
the  titration  of  zinc  ions,  after  the  removal  of  most  other  cations, 
with  ferrocyanide  ions  is  much  used.  The  method  is  a  good  one 
and  can  be  applied  without  difficulty  to  the  solution  from  which 
the  copper  and  lead  have  been  removed  by  electrolysis.  The 
titration  is  made  with  standard  potassium  ferrocyanide  solution 
in  a  solution  heated  to  at  least  60°  and  the  end-point  is  commonly 
determined  by  touching  with  uranium  solution  on  a  spot  plate. 
The  operator  has  to  practice  a  little  before  he  learns  is  to  distinguish 
the  true  end-point  and  the  method,  therefore,  to  be  recommended 
only  for  persons  who  are  experienced  and  such  chemists  will  not 
need  directions  here. 


332  CHEMICAL  ANALYSIS  OF  METALS 

The  electrolytic  determination  of  zinc  is  also  satisfactory 
but  unless  particular  pains  are  taken  the  results  are  likely  to  be 
a  little  high  owing  to  oxidation.  From  the  position  of  zinc  in 
the  electrochemical  series,  it  might  be  argued  that  this  metal 
could  not  be  deposited  upon  the  cathode  in  the  presence  of  free 
acid.  It  can  however,  be  deposited  from  acetic  acid  solutions 
containing  sodium  acetate,  because  of  the  overvoltage  that  zinc 
shows  toward  the  discharge  of  hydrogen. 

The  gravimetric  determination  of  zinc  after  precipitation  as 
zinc  ammonium  phosphate  is,  all  things  considered,  the  most 
satisfactory  method  for  determining  zinc  and  a  beginner  can 
follow  the  directions  and  get  accurate  results.  For  this  reason 
it  will  be  the  only  method  described. 

The  sole  difficulty  with  regard  to  the  determination  lies  in  the 
fact  that  nearly  all  other  metals,  except  the  alkalies,  form  insolu- 
ble phosphates.  Most  of  these  phosphates,  except  those  of 
copper,  cadmium,  zinc,  nickel  and  cobalt,  are  insoluble  in  an 
excess  of  ammonium  hydroxide. 

Fortunately,  in  the  analysis  of  bronze  and  brass  it  is  often 
safe  to  assume  that  none  of  these  elements  are  present,  when  it 
comes  to  the  determination  of  zinc. 

The  qualitative  separation  of  zinc  and  cadmium  is  usually 
accomplished  by  introducing  hydrogen  sulfide  into  0.3-normal 
hydrochloric  acid  solution.  If,  however,  a  large  quantity  of 
zinc  is  present  and  a  small  quantity  of  cadmium,  the  separation 
is  imperfect.  It  is  best  to  reduce  the  acid  concentration  so  that 
some  of  the  zinc  precipitates.  By  dissolving  the  precipitate  in 
hot  hydrochloric  acid,  diluting  and  repeating  the  precipitation 
twice  more  with  hydrogen  sulfide  in  approximately  2-normal  acid 
solution,  it  is  possible  to  detect  a  trace  of  cadmium  in  every  zinc 
alloy  provided  a  large  sample  of  the  metal  is  taken  for  analysis. 
Copper  should  be  absent  during  this  treatment,  although  its 
sulfide  will  not  dissolve  appreciably  in  the  hot  hydrochloric 
acid  and  is  merely  troublesome.  It  is  rarely  necessary,  however, 
to  determine  the  cadmium  content  as  the  quantity  usually 
present  in  alloys  is  insignificant.  A  cadmium  sulfide  precipitate 
can  be  converted  to  sulfate  by  sulfuric  acid  and  weighed  as  such 
in  a  porcelain  crucible. 

The  separation  of  zinc  from  iron,  nickel,  cobalt,  manganese  and 


NON-FERROUS  ALLOYS  333 

ions  of  the  alkaline  earth  group  can  also  be  accomplished  by 
means  of  hydrogen  sulfide,  Make  the  solution  left  after  the 
determination  of  copper  by  electrolysis,  alkaline  with  ammonium 
hydroxide,  add  enough  40  per  cent  formic  acid  to  make  the  solu- 
tion neutral  and  leave  5  c.c.  in  excess,  heat  the  solution  to  boiling 
and  precipitate  the  zinc  in  a  volume  of  about  300  c.c.  Filter 
and  wash  with  hot  water  containing  hydrogen  sulfide.  Zinc 
sulfide  precipitates  are  often  hard  to  filter  and  are  bulky.  By 
careful  roasting  in  a  porcelain  crucible  the  zinc  can  be  converted 
to  oxide  and  weighed  as  such;  this  method  is  suitable  when  the 
zinc  content  is  low.  With  considerable  zinc,  it  is  better  to  dissolve 
the  precipitate  in  hydrochloric  acid  and  precipitate  as  zinc 
ammonium  phosphate. 

It  is  a  matter  of  indifference  whether  the  zinc  ammonium 
phosphate  is  weighed  as  such,  after  drying  at  120  to  130°  or 
whether  it  is  ignited  carefully  in  a  weighed  porcelain  crucible  and 
weighed  as  zinc  pyrophosphate,  Zn2P207. 

In  precipitating  zinc  as  phosphate  it  is  important  to  remember 
that  zinc  ammonium  phosphate  dissolves  easily  in  dilute  hydro- 
chloric acid  and  in  dilute  ammonia  solution.  In  the  former  case, 
very  slightly  ionized  HPO4 —  is  formed  and  in  the  latter  case  very 
slightly  ionized  zinc  ammonia  ions,  Zn(NH3)4++  or  (Zn(NH3)6)++. 

Procedure. — Treat  the  cold,  acid  solution  obtained  after  the 
removal  of  the  copper  and  lead  by  electrolysis,  or,  by  the  dis- 
solving of  zinc  sulfide  in  hydrochloric  acid,  if  it  is  thought  nec- 
essary to  go  through  the  above-described  purification,  with  dilute 
ammonium  hydroxide  solution  until  it  is  left  barely  acid  to  lit- 
mus. Care  is  necessary  at  this  point.  Dilute,  if  necessary,  to 
about  150  c.c.  and  heat  on  the  water  bath.  To  the  hot  solution, 
add  10  times  as  much  diammonium  phosphate  as  there  is  zinc 
present.  (If  there  is  some  monoammonium  phosphate  in  the 
salt,  it  should  be  dissolved  in  a  little  cold  water  and  treated  with 
ammonium  hydroxide  solution  until  it  is  barely  ammoniacal  to 
phenolphthalein).  The  precipitate  is  amorphous  at  first  but 
becomes  crystalline  very  quickly,  when  heated  on  the  water  bath. 
The  transformation  takes  place  more  rapidly  in  proportion  to  the 
amount  of  ammonium  salts  present  and  it  is  well  to  add  2  or  3  g. 
of  ammonium  chloride.  After  heating  about  15  min.  remove 
the  beaker  from  the  bath  and  allow  the  precipitate  to  settle  for 


334  CHEMICAL  ANALYSIS  OF  METALS 

a  few  minutes.  Filter  the  solution  through  a  weighed  Gooch 
crucible  and  wash  the  precipitate  8  times  with  small  portions 
of  1  per  cent  ammonium  phosphate  solution,  twice  with  cold 
water,  and  once  with  50  per  cent  alcohol.  Dry  at  120  to 
130°  for  1  hr.  and  weigh  as  ZnNH4PO4  containing  36.34  per  cent 


zinc. 


PART  II 
THE  APPLICATION  OF  METALLOGRAPHY 

TO  THE 

INSPECTION  AND  SAMPLING  OF  ALLOYS 


CHAPTER  XXIII 
PREPARATION  AND  EXAMINATION  OF  THE  SPECIMEN 

The  ultimate  test  of  the  quality  of  a  metal  is  its  behavior  in 
actual  service,  or  at  least  under  conditions  which  approximate 
those  to  which  it  will  be  subjected  in  use.  Such  a  test  is  neces- 
sarily expensive  and  time-consuming,  and  can  only  be  resorted 
to  in  those  special  cases  where  absolute  knowledge  of  the  proper- 
ties of  the  material  outweighs  all  other  considerations.  In 
ordinary  practice,  shorter  and  cheaper  tests  must  be  used.  The 
modern  study  of  metals  has  shown  that  while  the  chemical 
composition  of  an  alloy  may  be  satisfactory,  the  metal  due  to 
improper  heat  treatment,  mechanical  treatment  or  both  may  be 
wholly  unsuited  for  use.  After  a  satisfactory  chemical  analysis 
of  the  sample  has  been  made  there  are  two  additional  questions 
to  answer.  (1)  Does  the  sample  truly  represent  the  material 
under  examination?  (2)  Does  the  chemical  analysis  give  all 
the  needed  information? 

With  regard  to  the  first  question,  if  the  material  contains 
segregated  areas,  as  for  example  a  bar  of  steel  with  areas  rich  in 
phosphorus,  a  sample  taken  at  random  might  represent  either 
a  high-phosphorus  or  a  low-phosphorus  area,  and  the  chemical 
analysis  may  be  of  little  value  regardless  of  its  correctness.  The 
analyst  can  be  held  responsible  only  for  the  accuracy  of  his 
methods,  unless  the  operation  of  sampling  is  placed  under  his 
control. 

The  second  question  may  be  illustrated  by  a  reference  to 
spring  brass,  whose  hardness  is  produced  by  mechanical  working 
of  the  cold  metal.  Hardness  or  brittleness,  caused  by  such 
mechanical  operations  as  rolling,  hammering  or  drawing,  cannot 
be  detected  by  chemical  analysis,  consequently  a  material  of 
excellent  chemical  composition  may  be  wholly  unsuited  for  a 
given  purpose  because  of  its  mechanical  condition. 

It  is  the  purpose  of  these  chapters  dealing,  for  the  most  part, 
with  the  microscopic  examination  of  metals,  to  consider  the 
22  337 


338  MICROSCOPIC  EXAMINATION  OF  METALS 

methods  of  metallography  as  they  may  be  applied  in  answering 
the  two  fundamental  questions  just  considered. 

It  is  not  possible  to  consider  the  subject  of  general  metal- 
lography1 here,  but  those  phases  of  it  which  are  of  direct  applica- 
tion to  the  microscopic  study  of  the  technical  alloys  are 
discussed  briefly. 

The  microscope  has  proved  itself  of  great  and  constantly 
increasing  usefulness,  not  only  as  an  aid  in  getting  representative 
samples  but  also  as  a  source  of  additional  information  concerning 
the  properties  of  the  metal  under  test.  No  attempt  is  made  to 
separate  these  two  uses  of  the  microscope,  as  the  general  character 
of  the  metal  determines  whether  or  not  special  precautions  are 
necessary  in  selecting  representative  samples  for  analysis. 
Microscopic  study  of  alloys  involves  several  factors;  preparation 
of  a  suitably  polished  surface,  development  of  the  internal 
structure  by  means  of  chemical  " etching  reagents"  or  in  some 
other  way,  the  arrangement  and  use  of  the  microscope  in  the 
examination  of  metals  and  finally  an  interpretation  of  the 
observations,  usually  with  reference  to  the  equilibrium  diagram 
(p.  356). 

Preparation  of  the  Specimen. — If  the  specimen  to  be  examined 
is  a  large  one,  as  for  example  a  broken  rail,  it  is  often  advantage- 
ous to  make  an  examination  of  a  roughly  polished  surface  without 
the  microscope  (macroscopic  examination)  in  order  to  determine 
the  particular  areas  which  need  more  careful  study.2  When  the 
suspected  areas  have  been  located,  portions  of  the  metal  are  sawed 
off  at  these  places,  the  size  of  the  specimen  being  determined  by 
the  nature  of  the  material. 

When  a  sample  has  been  selected,  the  specimen  is  prepared  for 
microscopic  examination  by  rubbing  one  or  more  surfaces  on  a 
series  of  abrasive  materials,  each  one  finer  than  the  one  which 
precedes  it,  until  a  scratch-free,  mirror  surface  is  obtained.  The 
exact  sequence  of  abrasives  is  determined  to  some  extent  by  the 
nature  of  the  material  to  be  examined,  but  the  general  method  is 

1  For  details  of  general  metallography  the  reader  is  referred  to  DESCH, 
Metallography;   GULLIVER,    Metallic  Alloys;   ROSENHAIN,   Physical    Metal- 
lurgy;  SAUVEUR,    Metallography   and  Heat    Treatment   of  Iron  and  Steel; 
WILLIAMS,  Principles  of  Metallography. 

2  Details  of  "macroscopic  examination"  are  given  on  p.  373. 


PREPARATION  AND  EXAMINATION  OF  THE  SPECIMEN     339 

as  follows.  If  the  material  is  hard,  like  steel,  grind  the  surface 
first  on  a  medium  emery  or  carborundum  wheel  and  then  on  a 
fine  one  taking  pains  to  hold  the  specimen  in  such  a  way  that  the 
scratches  produced  by  the  first  wheel  will  be  eliminated  by  the 
action  of  the  second.  If  the  sample  is  moderately  soft,  like 
brass  or  Babbitt  metal,  clamp  the  specimen  in  a  vise  and  file 
the  surface  flat  using  first  a  medium  and  then  a  fine  file.  The 
direction  of  filing  with  the  fine  file  should  be  at  right  angles 
to  that  of  the  coarse  file  and  the  operation  should  be  continued 
until  the  coarse  file  marks  have  been  removed.  It  is  a  general 
rule  that  when  a  specimen  is  being  polished  with  a  series  of 
abrasives  the  direction  of  polishing  with  each  abrasive  should  be 
at  approximately  right  angles  to  that  of  the  one  next  preceding 
it  and  that  the  polishing  should  be  continued  with  each  abrasive 
until  the  marks  produced  by  the  next  coarser  material  have 
been  wholly  eradicated. 

After  a  fairly  smooth  surface  has  been  obtained  by  grinding  or 
filing,  continue  the  polishing  operation  by  rubbing  the  surface 
on  a  succession  of  emery  cloths  or  papers,  each  one  finer  than  the 
one  before  it.  Many  kinds  of  emery  cloth  and  paper  are  avail- 
able, but  the  most  satisfactory  for  metallographic  purposes  is 
the  French  emery  paper  (Marke  Hubert).  If  French  emery 
paper  is  used,  transfer  the  ground  or  filed  specimen  to  the  grade 
1C,  next  to  IF  and  finally  to  0  and  00.  For  special  work  with 
very  soft  alloys,  the  finer  grades  000  and  0000  must  be  used  and, 
in  such  a  case,  either  the  specimen  or  the  emery  paper  must  be 
kept  moist  with  a  light  machine  oil  to  get  a  satisfactory  surface. 

After  as  good  a  surface  as  possible  has  been  obtained  with  the 
emery  papers,  continue  the  polishing  operation  by  rubbing  the 
specimen  on  cloths  which  have  been  treated  with  fine  abrasive 
powders,  applied  to  them  in  the  form  of  suspensions  in  water  or 
other  suitable  liquid.  Polishing  powders  of  this  sort  may  be 
obtained  from  any  dealer  in  metallographic  or  chemical  supplies. 
An  excellent  series  of  abrasives  for  this  special  use,  consisting 
of  various  grades  of  alundum  with  " levigated  alumina"  as  the 
final  polishing  medium,  has  been  prepared  by  the  Norton  Com- 
pany of  Worcester,  Massachusetts.  Rouge  is  often  used  and 
recommended  by  metallographers  as  the  finest  polishing  powder, 
but  although  it  gives  a  brilliant  polish,  it  has  a  tendency  to 


340 


MICROSCOPIC  EXAMINATION  OF  METALS 


cause  a  surface  flow  of  the  metal,  and  it  is  also  a  rather  dirty 
material  to  handle. 

The  cloth,  on  which  the  suspension  of  polishing  powder  is 
sprayed  or  sprinkled,  must  be  so  soft  that  it  will  not  itself 
scratch  the  softest  metal.  "Selvyt"  is  often  recommended  but 
the  less  expensive  broadcloth  known  as  "Lady  Cloth"  is 
satisfactory.  The  finest  quality  of  chamois  leather  has  been 
used  also.  When  the  polishing  is  to  be  done  by  hand,  the  cloths 
and  emery  papers  are  tacked  to  smooth  boards  about  3  by  8 
in.,  often  with  a  sheet  of  plate  glass  between  the  cloth  and  the 
board  backing  to  insure  an  absolutely  smooth  surface.  Machine 


FIG.  46. — Section  of  polishing  wheel. 

polishing  is  much  more  rapid  and  efficient,  and  many  excellent 
polishing  machines  of  various  types  are  now  on  the  market. 
Most  of  them  consist  of  disks  rotating  either  in  a  vertical  or  in  a 
horizontal  position,  a  few  consist  of  boards  which  move  back 
and  forth  in  a  horizontal  position  and  to  which  the  polishing 
cloth  or  paper  is  attached.  One  modern  type  is  composed  of 
series  of  interchangeable  cloth  endless  belts  which  move  over 
horizontal  cylinders  and  carry  the  different  polishing  substances. 
If  power  is  available  in  the  testing  laboratory,  it  is  a  simple 
matter  to  build  a  polishing  machine  in  the  way  indicated  in  the 
sketch,  Fig.  46.  The  disks  are  made  of  wood  or  brass  and  are 
provided  with  a  large  groove  in  the  outer  edge,  so  that  the 
tightly  stretched  cloth  can  be  held  in  place  by  a  band  of  wire  or 


PREPARATION  AND  EXAMINATION  OF  THE  SPECIMEN     341 

by  means  of  a  strong  elastic  band  or  spiral  spring.  The  wheels 
are  guarded  by  cast-iron  or  sheet-steel  cases  to  prevent  the 
liquid  polishing  materials  from  being  thrown  out  by  the  rotating 
wheel.  The  disks  are  5  or  6  in.  in  diameter,  and  should  rotate 
at  about  300  r.p.m.  Every  possible  precaution  should  be 
taken  to  prevent  the  transfer  of  coarse  polishing  powder  to 
a  wheel  to  be  used  for  fine  material.  A  single  grain  of  coarse 
material  on  the  final  wheel  may  necessitate  the  repolishing  of 
an  otherwise  perfect  specimen.  Suspended  abrasives  may  be 
applied  to  the  polishing  disks  by  means  of  an  ordinary  wash 
bottle,  be  blown  against  the  surface  by  an  ato- 
mizer or  be  shaken  on  the  surface  by  means  of 
the  simple  shaking  bottle  shown  in  Fig.  47. 
The  number  of  abrasive  powders  to  be  used  de- 
pends on  the  hardness  of  the  specimen  to  be 
polished,  but  for  most  technical  alloys  a  satis- 
factory surface  may  be  obtained  with  three; 
"60-min."  emery,  followed  by  "alundum  F"  and 
finally  by  levigated  alumina.  With  very  hard 
specimens  one  or  two  intermediate  grades  may 
be  found  necessary.  FIG.  47.— Flask 

Etching.— A  highly  polished  metal  surface  has  fa0brrasivseusspended 
little  or  no  characteristic  structure  under  the 
microscope,  unless  it  happens  to  be  composed  of  two  or  more 
metals  which  do  not  mix  in  the  solid  state  and  which  differ  in 
color,  or  unless  it  contains  slag  or  other  non-metallic  im- 
purities. It  is  necessary,  therefore,  to  treat  the  polished 
surface  in  such  a  way  that  the  different  constituents  of  the 
alloy  are  colored  differently,  or  that  one  constituent  is  more 
rapidly  dissolved  than  the  other,  producing  a  surface  which  is 
no  longer  smooth  but  covered  with  ridges  and  depressions, 
or  in  some  way  producing  a  contrast  between  the  compo- 
nents, of  the  metal.  This  operation  is  called  "  etching"  and  is 
usually  a  selective  chemical  action.  The  particular  reagent 
to  be  used  to  develop  the  surface  structure  depends  on  the 
composition  and  physical  characteristics  of  the  alloy  under 
examination.  Although  a  large  number  of  reagents  have  been 
used  for  various  purposes,1  the  study  of  the  industrial  alloys 

1  Cf.  Zeitshrift  fur  Metallkunde,  8,  228  (1916). 


342 


MICROSCOPIC  EXAMINATION  OF  METALS 


To.  Eye 
Piece  or 
Camera 

A    A    A 


requires  only  a  small  number  of  solutions.  Dilute  acids  or 
alkalis  are  often  used  for  general  purposes,  the  particular  reagent 
depending  on  the  solubility  of  the  constituents  of  the  alloy  to  be 
studied.  A  solution  of  10  g.  of  ferric  chloride  (FeCl3)  in  100  c.c. 
of  alcohol  is  a  useful  reagent  for  many  of  the  non-ferrous  alloys. 
The  special  reagents  which  are  commonly  used  in  the  examination 
of  steels,  brasses,  bronzes  and  Babbitt  metal  are  described  in  con- 
nection with  the  discussion  of  these  important  industrial  alloys. 
The  Microscope. — For  the  examination  of  polished  and  etched 
metal  specimens,  a  type  of  microscope  is  needed,  with  which 
the  specimen  may  be  examined  by  reflected  instead  of  transmitted 
light.  A  "  vertical  illuminator,"  the  principle  of  which  is  shown 
in  the  following  sketch  (Fig.  48)  can  be  obtained  from  any  dealer 
in  optical  apparatus  at  a  moderate  ex- 
pense and  may  be  fitted  to  an  ordinary 
microscope.  The  source  of  light  may  be 
a  small  arc,  a  nitrogen-filled  tungsten 
incandescent  lamp  or  any  other  lamp 
giving  a  brilliant  illumination  which  can 
be  concentrated  by  means  of  a  con- 
densing lens.  An  outfit  of  this  type  is 
quite  satisfactory  for  most  of  the  micro- 
scopic work  of  a  small  laboratory  and  can 
be  assembled  at  a  small  cost.  If  much 
microscopic  work  is  to  be  done  and 
especially  if  a  photographic  record  is  to 
be  kept,  one  of  the  many  excellent 
photomicrographic  cameras  will  be  found 
indispensable.  All  are  alike  in  principle 
and  consist  of  a  train  of  lenses  and  mir- 
rors, so  arranged  that  a  magnified  image 
of  an  illuminated  spot  on  the  polished 
metal  surface  is  transmitted  either  to  the  observer's  eye  for  im- 
mediate examination  or  to  a  photographic  plate  for  permanent 
record.  The  following  standard  magnifications  for  use  in  examin- 
ing metals  and  in  the  preparation  of  photomicrographs  have  been 
adopted  by  the  American  Society  for  Testing  Materials: 
10,  25,  50,  75,  100,  200,  500,  and  1,000  diameters1 
See  p.  464  for  magnifications  used  in  studying  grain  size. 


To 

Objective 

.and 

Polished 
Specimen 

FIG.  48. — Sketch  of  verti- 
cal illuminator  (sheet  glass 
type)  dotted  lines  show  the 
direction  of  rays  reflected 
from  the  specimen. 


PREPARATION  AND  EXAMINATION  OF  THE  SPECIMEN     343 

The  magnifications  indicated  represent  the  actual  magnifica- 
tion of  the  image  as  recorded  on  the  photographic  plate,  and  the 
general  adoption  of  these  values  would  be  of  great  help  in  com- 
paring the  results  obtained  by  different  observers  on  metals  of  the 
same  class. 

For  the  general  examination  of  large  areas  on  a  specimen, 
rather  than  the  detailed  examination  of  a  small  area,  a  microscope 
like  that  shown  in  Fig.  49  is  useful.  Several  instruments  of  this 
sort  are  on  the  market. 


FIG.  49. — Low-powered  microscope  for  examination  of  large  areas. 

Photographing  the  Specimen. — If,  as  is  often  the  case,  a  per- 
manent record  of  the  defective  material  is  to  be  kept,  the  metal- 
microscope  is  provided  with  a  photographic  attachment.  The 
actual  operation  of  taking  the  picture  depends  on  the  mechanical 
construction  of  the  particular  instrument  used,  so  that  details 
cannot  be  given  here,  but  the  process  is  not  difficult  and  may  be 
learned  with  very  little  practice.  The  plates  used  for  the  pur- 
pose must  be  fine  grained,  and  for  the  brasses  and  bronzes  must  be 
color  sensitive.  " Wellington  Ortho  Process  Plates"  have  been 
found  satisfactory  for  all  purposes,  but  for  the  photography  of 
steel  specimens,  where  color  sensitiveness  is  of  minor  importance, 
the  much  less  expensive  " Stanley"  plates  may  be  used.  Other 
plates  which  have  been  used  successfully  for  photomicrographic 
work  are  the  "Wratten  M,"  " Standard  Orthonon,"  ''Cramer 


344  MICROSCOPIC  EXAMINATION  OF  METALS 

Contrast"  and  "Imperial  Standard."  Any  one  of  the  standard 
process  plates  would  no  doubt  be  found  satisfactory  for  the 
purpose.  When  colored  alloys  like  brass  and  bronze  are  photo- 
graphed, it  is  usually  necessary  to  use  a  color  screen  in  order  to 
produce  the  needed  contrast.  A  yellowish-green  screen  gives 
good  results  with  the  copper  alloys,  though  some  operators  prefer 
a  deep  orange  or  even  a  red  screen  for  the  purpose.  The  screen 
is  held  in  position  between  the  source  of  light  and  the  vertical 
illuminator.  The  time  of  exposure  of  the  plate  varies  from  a  few 
seconds,  with  the  unscreened  light  from  an  arc  lamp,  to  30  min. 
or  more,  with  a  less  powerful  light  source  and  a  deeply  colored 
screen,  and  can  only  be  determined  by  experience.  Certain  of 
the  modern  metallographic  cameras  are  provided  with  an  auto- 
matic plate  holder  by  means  of  which  a  series  of  exposures  of 
different  lengths  may  be  made  on  a  single  plate.  After  develop- 
ment the  most  suitable  exposure  time  can  be  selected  from  the 
series  so  that  later  photographs  taken  under  similar  conditions 
can  then  be  correctly  exposed.  If  such  an  automatic  device  is 
not  available,  the  same  information  can  be  obtained  in  the 
following  way:  Expose  the  plate  as  usual  for  a  short  interval, 
then  push  in  the  opaque  slide,  which  is  used  to  cover  the  plate  in 
its  holder,  about  J^  in.  in  order  to  shut  off  a  portion  of  the  exposed 
plate.  Make  a  second  exposure  and  push  the  slide  in  again 
another  short  distance.  Repeat  the  operation,  shutting  off 
about  a  J^-in.  strip  of  the  plate  each  time  from  the  action  of  the 
light,  until  the  opaque  screen  has  been  returned  to  its  final  posi- 
tion in  the  holder.  Develop  the  exposed  plate  and  a  series  of 
bands  will  be  found  each  of  which  represents  a  longer  exposure 
than  the  one  next  to  it,  and  from  the  time  required  to  produce  the 
band  which  shows  the  best  detail,  estimate  the  suitable  exposure 
time  for  specimens  of  the  same  general  character  using  plates  of 
the  same  speed. 

Photomicrographs  should  be  printed  on  glossy  paper  in  order  to 
bring  out  the  fine  details  of  the  structure.  Glossy  Velox,  Glossy 
Cyko  or  other  papers  of  the  same  type  are  commonly  used  and 
the  best  results  are  obtained  if  the  prints  are  dried  on  a  ferrotype 
plate.  Unless  special  precautions  are  taken  in  the  preparation 
of  the  ferrotype  plate  for  use,  much  annoyance  will  be  caused  by 
the  sticking  of  the  prints  to  the  polished  surface.  The  usual 


PREPARATION  AND  EXAMINATION  OF  THE  SPECIMEN     345 


z 

2       D. 


Z      O 


I     Q 


•3  H 

Q>  0} 

^  -P 

fc  ra 

o  >> 

>  tl 


O 
P 


C  oj 

•H 

I  I 

CO  *-> 


a: 
o 


346  MICROSCOPIC  EXAMINATION  OF  METALS 

causes  of  the  difficulty  are  incompletely  washed  prints  or  an  in- 
sufficiently polished  surface  of  the  plate.  Clean  the  surface  of 
the  ferrotype  plate  thoroughly  with  warm  water  or  alcohol,  and 
then  cover  it  with  a  very  thin  layer  of  wax  applied  to  the  surface 
in  the  form  of  a  solution  of  beeswax  in  benzene  or  use  one  of  the 
solutions  prepared  for  the  purpose,  such  as  the  Ingento  Polishing 
Compound.  Let  the  plate  stand  for  a  few  minutes  until  the  sol- 
vent has  evaporated,  leaving  the  waxed  surface,  and  then  rub 
vigorously  until  the  excess  wax  has  been  removed  and  a  brilliant 
polish  results.  Five  or  six  drops  of  the  polishing  solution  is 
enough  for  the  purpose. 

If  many  photographs  are  to  be  preserved,  some  sort  of  a  card 
on  which  the  prints  can  be  mounted  for  filing  is  useful.  Figure 
50  shows  a  style  of  mount  suitable  for  general  purposes. 


CHAPTER  XXIV 

THE  METALLOGRAPHIC  CONSTITUENTS  OF  IRON 
AND  STEEL 

Although  it  is  not  necessary  to  consider  in  detail  the  many 
changes  which  may  take  place  when  melted  alloys  solidify,  the 
changes  which  occur  during  the  heating  and  cooling  of  iron-car- 
bon alloys  (iron  and  steel)  have  such  an  important  bearing  on 
their  physical  properties,  that  the  equilibrium  diagram  of  these 
alloys  will  be  considered  briefly,  as  it  indicates  graphically  the 
condition  in  which  the  alloys  exist  at  different  temperatures  and 
with  varying  carbon  content.  In 
order  to  make  the  fairly  complex 
iron-carbon  diagram  more  clearly 
understood,  it  is  perhaps  worth 
while  to  discuss  some  of  the 
simpler  types  of  alloy  diagrams, 
of  which  the  steel  diagram  is  a 
composite. 

The  Eutectic  Alloy.— When  a 
pure  metal  solidifies  from  the 
melted  condition  and  the  temper- 
ature changes  which  take  place 
during  the  cooling  are  indicated 
in  a  graphical  form,  a  curve,  in 
which  temperatures  are  repre- 
sented as  ordinates  and  time  in- 
tervals between  temperature  read- 
ings as  abscissas,  may  be  con- 
structed (Fig.  51).  The  solidification  of  lead  has  been  selected  as 
an  example,  with  intervals  of  10  sec.  between  each  temperature 
reading.  It  will  be  noticed  that  the  curve  falls  smoothly  until 
the  temperature  of  327°C.  is  reached,  when  it  breaks  sharply  and 
remains  horizontal,  indicating  a  constant  temperature  during  an 
appreciable  period.  The  curve  again  falls  gradually  to  room 

347 


327 


FIG. 


Time  in  .Seconds 

51. — Cooling    curve    of    pure 
lead. 


348 


MICROSCOPIC  EXAMINATION  OF  METALS 


temperature  without  further  abrupt  changes  in  direction.  The 
horizontal  line  represents'  the  transition  of  the  lead  from  the 
liquid  to  the  solid  state.  It  is  a  well-known  fact  that  in  most 
cases  in  which  one  substance  is  added  to  another,  in  which  it 
will  dissolve,  the  freezing  point  of  the  solvent  is  lowered  percepti- 
bly. A  common  illustration  of  this  phenomenon  is  the  prepara- 
tion of  the  ice-salt  freezing  mixture  which  can  produce  a 
temperature  —  21°  C.  Numerous  alloys  behave  in  the  same  way; 
one  of  the  best  known  of  which  is  that  of  lead  with  antimony.  If  a 
small  amount  of  lead  is  added  to  molten  antimony,  the  freezing 
point  of  the  latter  is  lowered  and  increasing  quantities  of  lead 


Pb 

327' 
248* 


1  =  90  %  Pb 

2  =  87.5%  , 


Sb, 


FIG.  52. — Lead-antimony  cooling  curves. 

still  further  lower  the  freezing  point.  If,  on  the  other  hand, 
antimony  is  added  to  pure  lead  the  melting  point  of  the  lead  is 
lowered  and,  as  in  the  case  of  antimony,  is  progressively  lowered 
by  the  addition  of  greater  quantities  of  antimony.  The  effect 
of  the  addition  of  each  metal  to  the  other  is  shown  in  the  series 
of  curves  of  Fig.  52.  It  is  obvious  that  since  each  metal  lowers 
the  freezing  point  of  the  other,  the  lines  connecting  these  freezing 
points  must  intersect  at  some  point  as  shown  by  the  dotted  lines 
in  the  drawing,  Fig.  52.  This  point  is  called  the  eutectic  point, 
the  alloy  corresponding  to  the  intersection  of  the  two  lines  the 
eutectic  alloy  and  the  temperature  at  which  the  lines  cross,  the 
eutectic  temperature.  If  the  data  given  by  the  cooling  curves  of 
Fig.  52  is  assembled  in  the  form  of  an  equilibrium  diagram,  the 


METALLOGRAPHIC  CONSTITUENTS  OF  IRON  AND  STEEL  349 

diagram  takes  the  form  indicated  in  Fig.  53  in  which  the  ordinates 
are  temperatures  and  the  abscissas,  percentage  compositions 
of  the  series  of  alloys  studied.  The  lines  PbB  and  SbB  together 
form  the  freezing  point  diagram,  as  the  freezing  points  of  all 
lead-antimony  alloys  lie  on  this  V-shaped  curve.  The  line  DBE 
indicates  the  temperature  at  which  the  second  heat  effect  occurs 
in  all  alloys  of  this  series  and  corresponds  to  the  horizontal  lines 
in  Fig.  52.  DBE  is  called  the  eutectic  line.  The  meaning  of  a 
diagram  of  this  type  can  be  understood  more  readily  by  consider- 
ing the  physical  changes  which  take  place  in  a  few  special  cases  as, 
for  example,  during  the  cooling  of  alloys  1,  2,  3,  in  Fig.  53.  Since 


tb    90 


50 
Composition 


30 


10    Sb 


FIG.  53. — Lead-antimony  diagram. 


the  F -shaped  curve  was  obtained  by  connecting  the  freezing 
points  of  the  separate  alloys,  it  is  evident  that  the  area  above  the 
V  represents  a  temperature  range  in  which  everything  is  in  the 
molten  condition.  As  the  temperature  of  alloy  1  falls,  no  change 
takes  place  until  the  line  PbB  is  reached,  when  pure  lead  begins 
to  separate.  The  result  of  the  separation  is  to  leave  a  solution 
richer  in  antimony  than  the  original  and,  therefore,  one  which 
has  a  lower  freezing  point.  Pure  lead  continues  to  separate  with 
the  consequent  formation  of  solutions  increasingly  richer  in 
antimony  and  therefore  with  lower  freezing  points.  As  the  liquid 
from  which  the  lead  is  separating  becomes  richer  in  antimony  it 
approaches  the  eutectic  composition  indicated  by  B.  Since  this 


350 


MICROSCOPIC  EXAMINATION  OF  METALS 


represents  the  lowest  possible  temperature  at  which  any  lead  and 
antimony  alloy  can  solidify,  it  is  evident  that  when  the  residual 
liquid  finally  reaches  the  eutectic  composition,  the  remaining  metal 
will  solidify  at  this  constant  temperature.  The  same  reasoning 
applies  to  alloy  3  except  that  in  this  case  the  antimony  crystals 
separate  first.  The  primary  separation  of  antimony  is  followed 
by  an  enrichment  of  the  remaining  liquid  with  lead  until  the 
eutectic  composition  is  reached  again.  At  the  composition  re- 
presented by  alloy  2  no  change  takes  place  until  the  eutectic 

temperature  is  reached 
when  lead  and  antimony 
separate  together  in  the 
form  of  the  eutectic  mix- 
ture. If  equal  weights 
of  the  mixture  of  the  two 
metals  were  taken  for 
each  alloy  indicated  on 
the  diagram,  the  number 
of  seconds  taken  for  the 
liquid  of  eutectic  com- 
position to  solidify  would 
depend  on  the  amount  of 
material  of  this  compo- 
sition present  in  each 
case.  This  would  be 
greatest  at  the  compo- 
sition B,  where  only  eutectic  is  found,  and  would  decrease 
right  and  left  from  this  point,  as  the  excess  of  antimony  or  lead 
over  the  eutectic  composition  increased.  The  shortening  of  the 
time  for  the  solidification  of  the  alloy  of  eutectic  composition  is 
indicated  in  the  triangular  area  marked  "Time"  in  the  upper 
part  of  Fig.  53. 

Because  of  the  constant  temperature  at  which  the  eutectic 
separates,  it  was  formerly  believed  that  the  eutectic  was  a  com- 
pound. The  microscope  shows  clearly  that  this  is  not  the  case, 
but  that,  on  the  contrary,  the  eutectic  alloy  is  an  extremely  inti- 
mate mixture  of  the  two  component  metals.  (See  Fig.  54,  the 
eutectic  of  bismuth-tin  with  a  slight  excess  of  tin.)  Since  the 
eutectic  is  a  mixture  of  the  two  metals  and  since,  as  shown  in  the 


FIG.    54. — Bismuth-tin    eutectic   containing  a 
slight  excess  of  tin.'    (Sawyer.) 


METALLOGRAPHIC  CONSTITUENTS  OF  IRON  AND  STEEL  351 

diagram,  Fig.  53,  the  eutectic  line  extends  from  one  side  of  the 
diagram  to  the  other,  it  follows  that  while  lead  and  antimony  are 
wholly  miscible  and  soluble  in  each  other  in  the  liquid  state,  they 
are  wholly  non-miscible  or  insoluble  in  each  other  in  the  solid 
state.  That  the  metals  are  insoluble  in  each  other  in  the  solid 
state  must  be  true  for  the  diagram  shows  that  no  matter  how  small 
an  amount  of  either  metal  is  added  to  the  other,  there  is  always 
the  secondary  heat  effect  at  the  eutectic  temperature.1 

The  Solid  Solution. — A  second  relationship  which  may  exist 
between  metals  and  one  of  the  greatest  importance  in  connection 
with  steel,  is  a  partial  or  complete  solubility  of  one  metal  or  ele- 
ment in  another,  in  the  solid  state  as  well  as  when,  the  metals  are 
molten.  This  relation  is  known  as  the  formation  of  a  solid  solu- 
tion. The  solid  solution  differs  from  the  liquid  solution  simply  in 
its  physical  condition.  Like  the  liquid  solution,  it  is  perfectly 
homogeneous  and  may  be  saturated  or  unsaturated.  Metal  A 
may  retain  10  per  cent  of  metal  B  in  the  solid  state,  but  if  an 
attempt  is  made  to  add  12  per  cent  of  B,  the  solid  solution  which 
separates  on  cooling  is  a  saturated  solution  of  10  per  cent  B 
in  A.  The  excess  B  remains  in  the  liquid  to  separate  later  as  a 
part  of  a  eutectic  mixture,  as  a  constituent  of  an  intermetallic 
compound  or  in  some  other  form.  This  conception  of  the  solid 
solution  as  wholly  analagous  to  the  liquid  solution  makes  the 
graphical  representation  easier  to  understand. 

Consider  as  an  example  the  diagram  of  the  alloys  of  copper  and 
silver,  Fig.  55.  This  differs  from  the  simple  eutectic  diagram 
shown  in  Fig.  53  only  in  the  location  on  it  of  the  lines  Ag-a  and 
Cw-j3,  the  significance  of  which  is  merely  that  molten  silver,  in 
which  copper  has  been  dissolved,  is  able  to  retain  about  6  per  cent 
of  copper  after  the  silver  has  solidified  and  that  molten  copper  in 
its  turn,  is  capable  of  retaining  an  equal  amount  of  silver  in  the  solid 
state.  When  an  alloy  of  silver  and  copper  containing  less  than 
29  per  cent  of  copper  is  allowed  to  solidify,  the  crystal  which  first 
separates  is  not  the  pure  element,  as  in  the  case  of  the  separation 
of  lead  in  the  cooling  of  the  lead  antimony  alloys,  but  is  a  homo- 
geneous, crystalline  solution  of  copper  in  silver.  The  meaning 

1  It  is  probably  not  true  that  any  two  metals  are  absolutely  insoluble  in 
each  other  in  the  solid  state  but  the  solubility  in  many  cases  is  so  slight  that 
it  cannot  be  detected  by  the  usual  temperature  measurements. 


352 


MICROSCOPIC  EXAMINATION  OF  METALS 


of  the  diagram,  then,  is  as  follows :  Any  alloy  of  silver  and  copper 
containing  less  than  6  per  cent  of  copper  on  the  one  hand,  or  less 
than  6  per  cent  or  silver  on  the  other,  will  solidify  as  an  unsat- 
urated  solid  solution  which  is  perfectly  homogeneous  and  under 
the  microscope  shows  only  the  fine  polyhedral  lines  characteristic 
of  a  single  crystalline  solid,  Fig.  161,  p.  454.  If  now,  the  amount 
of  copper  added  to  the  silver  is  ever  so  slightly  in  excess  of  6  per 
cent,  the  solid  alloy  is  no  longer  homogeneous  but  shows  a  second 
structure  element,  in  this  case  the  eutectic  E.  It  is  evident,  then, 
that  in  the  range  between  the  points  a  and  /3,  the  diagram  is  exactly 


FIG.  55. — Copper-silver  diagram.     (Heycock  and  Neville,  Fredrick  and  Leroux.) 

analagous  to  the  simple  eutectic  diagram,  the  only  difference 
being  that  with  the  silver  and  copper  alloys  the  constituents  are 
not  the  pure  metals  but  are  the  saturated  solid  solutions  o  and  /3. 
The  solubility  of  one  metal  in  another  may  increase  as  shown  in 
the  series  of  diagrams  of  Fig.  56,  until  the  condition  indicated  in  D 
is  realized.  The  line  a-(3  representing  the  secondary  or  eutectic 
separation,  has  gradually  shortened,  with  the  increase  in  the 
mutual  solubility  of  the  two  metals,  until  in  the  alloy  D  the  line 
has  disappeared  wholly,  showing  that  the  metals  are  soluble  in 
each  other  in  all  proportions  in  the  solid  state.  Diagrams  A 
and  D  differ  radically  in  this  respect,  although  both  show 


METALLOGRAPHIC  CONSTITUENTS  OF  IRON  AND  STEEL  353 


the  two  metals  to  be  soluble  in  each  other  in  all  proportions  in  the 
liquid  state  and,  also,  that  each  metal  lowers  the  melting  point  of 
the  other,  diagram  A  indicates  that  the  two  metals  are  completely 
insoluble  in  each  other  in  the  solid  state  while  diagram  D  shows 
that  the  two  solid  metals  are  soluble  in  each  other.  Alloy 
E  in  diagram  A  is  as  inhomogeneous  as  possible  while  a/3  in 
diagram  D  is  perfectly  homogeneous  and  represents  simply  that 


C  D 

FIG.  56. — Development  of  the  solid  solution. 

one  of  a  series  of  perfect  solutions  which  has  a  melting  point 
lower  than  that  of  any  of  the  other  solid  solutions  in  the  series. 
This  is  often  referred  to  as  the  solid  solution  minimum.  A 
second  type  of  solid  solution  includes  that  class  of  alloys  in 
which  the  metals  are  mutually  soluble  in  all  proportions  but 
whose  diagram  shows  no  minimum.  A  relation  of  this  sort  is 
shown  in  the  diagram  of  the  copper-nickel  alloys,  Fig.  57.  In 

23 


354 


MICROSCOPIC  EXAMINATION  OF  METALS 


addition  to  the  types  of  alloys  indicated  in  Figs.  53,  55  and  57, 
various  other  reactions  may  take  place  in  the  cooling  of  a  mixture 
of  metals  from  the  molten  state  as,  for  example,  the  formation 
of  one  or  more  intermetallic  compounds  or  a  partial  separation 
into  liquid  layers.  A  discussion  of  these  other  types  belongs  to 
the  field  of  general  metallography  and  has  no  immediate  con- 
nection with  the  present  problem. 


8|0    7|0    C|0    5|0    4|0    3|0 


FIG.  57.  —  Copper-nickel  alloys.     (Guertler  and  Tamman.) 

Changes  in  the  Solid  Alloy.  —  The  diagrams  which  have  been 
considered,  have  dealt  with  changes  which  occur  when  the  alloy 
passes  from  the  liquid  to  the  solid  state  or  vice  versa.  Some  of  the 
most  valuable  technical  alloys,  notably  steel,  acquire  their  proper- 
ties or  modify  them  materially  because  of  changes  which  take 
place  in  the  solid  state.  Iron,  for  example  is  believed  to  exist 
in  at  least  three  allotropic  forms  a-iron  stable  below  780°C., 
0-iron  existing  between  780  and  900°C.  and  finally  y-iron  stable 
above  900°C.  and  practically  non-magnetic.  While  these  mag- 
netic changes  are  of  interest  to  the  physicist,  the  fact  of  importance 
to  the  metallographer  is  that  y-iron  will  hold  carbon  in  solid  solu- 
tion but  a-  and  0-iron  will  not.  This  means  then,  that  when 
the  iron-carbon  alloy  is  cooled,  a  change  in  components,  and 
therefore  in  physical  properties,  occurs  in  passing  from  the  y-iron 
range  to  the  a-iron  range  even  though  the  alloy  in  the  y-field 
is  perfectly  solid. 

More  important  than  the  changes  due  to  the  allotropism  of  a 
single  metal  are  those  changes  which  come  from  the  decomposi- 
tion of  a  solid  solution  at  temperatures  below  its  freezing  point. 
All  the  changes  which  can  take  place  when  a  liquid  solution 


METALLOGRAPHIC  CONSTITUENTS  OF  IRON  AND  STEEL  355 


freezes  may  also  occur  when  a  solid  solution  decomposed.  It 
may  change  to  a  eutectic-like  mixture,  to  another  solid  solution 
more  or  less  complete  or  it  may  decompose  to  form  one  or  more 
compounds.  Some  of  these  possible  changes  are  indicated 
in  Fig.  58.  The  most  important  of  these  transformations  in  the 
solid  state  is  that  shown  in  I  of  the  figure,  as  many  of  the  valuable 
properties  of  steel,  given  to  it  by  heat  treatment,  are  due  to 
decompositions  of  this  sort.  Transformation  of  a  solid  alloy  of 
the  solid  solution  type  to  one  of  a  different  character,  requires 
a  definite  amount  of  time,  and  by  shortening  this  time,  the  trans- 
formation can  be  partially  or  wholly  suspended.  For  example, 
by  suddenly  cooling  (quenching)  an  alloy  from  the  temperature 
indicated  by  x  in  Fig.  58,  I,  it  is  possible  to  prevent  the  trans- 


FIG.  58. — Types  of  changes  occurring  in  the  solid  state. 

formation,  of  the  solid  alloy  along  AE,  into  that  represented 
by  xf,  with  the  result  that  at  ordinary  temperatures  the 
alloy  exists  in  the  condition  which  it  had  at  the  higher  tempera- 
ture x.  The  physical  properties  of  a  solid  solution  are  so  dif- 
ferent from  those  of  the  eutectic-like  mixture  that  by  more  or  less 
completely  checking  the  change  from  x  to  x'  the  mechanical 
properties  of  the  alloy  can  be  profoundly  modified  and  can  be 
controlled  within  fairly  definite  limits.  The  alloy  represented 
by  the  point  E,  Fig.  58,  I,  has  all  the  characteristics  of  the  eutec- 
tic  including  the  " thumb  print"  structure  as  seen  under  the 
microscope.  Since,  however,  the  separation  of  the  constituents 
takes  place  from  a  solid  solution,  instead  of  from  a  liquid,  the 
name  eutectoid  is  commonly  given  to  it. 


356 


MICROSCOPIC  EXAMINATION  OF  METALS 


Bearing  in  mind  the  significance  of  the  several  types  of  alloy 
diagrams  just  considered,  the  interpretation  of  the  iron-carbon 
diagram,  Fig.  59,  is  not  difficult  as  it  will  be  seen  to  contain  (1) 


solid  solutions  in  the  area  FeFPB,  (2)  the  eutectoid  P,  and  (3) 
the  eutectic  E,  the  two  components  of  which  are  the  saturated 
solid  solution  B  and  the  substance  which  separates  along  the  line 


METALLOGRAPHIC  CONSTITUENTS  OF  IRON  AND  STEEL  357 

CE,  which  in  this  case  is  not  pure  carbon  but  a  compound  which 
has  been  shown  by  chemical  analysis  to  have  the  symbol  Fe3C. 
The  same  compound  separates  along  the  line  BP  and  is  one  of  the 
two  components  of  the  eutectoid  P,  of  which  pure  iron  is  the 
other  constituent.  The  diagram  indicates  that  iron  will  dissolve 
carbon  with  the  formation  of  a  solid  solution,  which  becomes 
Saturated  when  the  carbon  content  has  reached  approximately 
1.7  per  cent.  The  area  FeFPB  includes  the  steels,  while  the 
cast  and  pig  iron  range  includes  the  iron-carbon  alloys  varying  in 
composition  from  1.7  per  cent  carbon  up  to  5  or  6  per  cent.  The 
single  exception  to  this  classification  is  the  wrought  iron 
(p.  367)  whose  carbon  content  is  commonly  less  than  0.3 
per  cent.  In  the  steel  section  of  the  diagram,  the  solid  solution 
included  in  the  area  FeFPB  decomposes  along  the  lines  FP 
and  PB  into  various  mixtures  of  pure  iron  (ferrite)  and  the 
eutectoid  P,  when  the  carbon  content  is  less  than  0.85  per  cent, 
or  into  iron  carbide  (Fe3C)  and  the  same  eutectoid,  when  the 
percentage  of  carbon  is  greater  than  that  shown  by  the  point 
P.  If  such  decomposition  always  took  place,  regardless  of  the 
cooling  rate,  there  would  be  only  three  classes  of  steel,  (1)  pure 
iron  with  varying  amounts  of  the  eutectoid  P,  (2)  the  eutectoid 
itself  and  (3)  ferric  carbide  with  varying  amounts  of  the  eutectoid, 
and  the  study  of  steel  would  be  a  comparatively  simple  matter. 
The  valuable  properties  of  steel  and  the  fact  that  its  properties 
can  be  profoundly  changed  by  heat  treatment  are  due  to  the 
slow  decomposition  of  the  solid  solution  into  its  final  components. 
This  gives  to  the  steel  maker  the  power  of  controlling  the  amount 
of  decomposition  to  a  marked  degree,  by  means  of  cooling  and 
heating  operations,  such  as  quenching,  tempering  and  annealing. 
If  the  solid  solution  could  be  kept  wholly  unchanged  by  suffi- 
ciently rapid  cooling  (quenching),  the  component  to  which  the 
name  Austenite  has  been  given  would  be  found.  This  can  hardly 
be  done  with  plain  carbon  steel,  though  austenite  is  a  common 
constituent  of  steels  containing  manganese,  nickel  and  other 
metals.  In  practice,  quenching  commonly  produces  the  first 
stage  in  the  decomposition  of  austenite  on  its  way  to  the  eutec- 
toid, and  the  resulting  material  has  been  called  Martensite. 
Still  slower  cooling  or,  more  commonly  in  practice,  reheating, 
leads  to  the  formation  of  Troostite,  which  in  its  turn  is  followed 


358  MICROSCOPIC  EXAMINATION  OF  METALS 

by  Sorbite  and  finally,  very  slow  cooling  of  the  steel  produces 
the  last  stage  in  the  decomposition  of  the  solid  solution,  namely 
the  eutectoid  Pearlite.  The  transition  briefly  stated  is  Austenite 
— »Martensite— »Troostite— ^Sorbite— ^Pearlite.  Pure  iron  which 
separates  along  the  line  FP  is  called  Ferrite,  and  iron  carbide  is 
known  as  Cementite.  A  brief  description  of  these  constituents 
with  the  methods  of  their  formation  will  be  given  shortly.  The 
constituents  of  cast  iron  vary  considerably  with  the  method  of 
production  of  the  iron  and  with  the  constituents  other  than 
carbon  which  may  be  present.  The  components  not  usually  found 
in  steel  are  Graphite  and  Graphitic  temper  carbon  and  the  eutectic 
E,  known  as  Ledeburite,  though  this  component  is  not  often 
named. 

Etching  of  Steel  and  Iron. — Many  more  or  less  complex 
solutions  have  been  tried  for  the  etching  of  steel,  but  for  the 
purposes  of  the  control  laboratory  a  few  of  the  simpler  ones  will 
serve  every  purpose. 

Nitric  A  cid  and  A  Icohol. — The  most  useful  of  all  etching  reagents 
for  steel  is  a  solution  containing  4  c.c.  of  concentrated  nitric 
acid  (d.  1.42)  in  96  c.c.  of  ethyl  alcohol.  The  specimen  is 
immersed  face  up  in  the  solution  and  is  kept  in  constant  motion 
to  prevent  the  formation  of  gas  bubbles  on  the  polished  surface. 
The  time  required  for  etching  varies  from  2  to  3  sec.  with  troostite, 
requires  about  5  sec.  for  martensite  and  from  7  to  10  sec.  for 
sorbite  and  pearlite.  After  the  specimen  is  etched,  it  is  dried 
with  a  soft  cloth  or  with  a  warm  blast  of  air. 

Picric  Acid. — A  solution  of  5  g.  of  picric  acid  in  95  c.c.  of  ethyl 
alcohol  is  often  used  for  low-carbon  steels. 

Alcoholic  Hydrochloric  Acid  recommended  by  Martens  and 
Heyn,  is  made  by  dissolving  1  c.c.  of  concentrated  hydrochloric 
acid  (d.  1.19)  in  100  c.c.  of  alcohol.  This  reagent  requires 
that  the  sample  be  immersed  from  six  to  eight  times  as  long  as 
with  nitric  acid  but  gives  excellent  results. 

Kourbatojf's  Reagent  for  Cementite. — Cementite  is  not  attacked 
by  the  usual  etching  reagents,  but  is  colored  black  or  brown  by 
immersion  for  a  period  of  3  to  5  min.  in  a  boiling  solution  of 
sodium  picrate  in  sodium  hydroxide.  The  reagent  is  made  by 
dissolving  2  g.  of  sodium  picrate  in  98  c.c.  of  a  25  per  cent  solution 
of  sodium  hydroxide.  Ferrite  is  not  affected  by  this  reagent  so 


METALLOGRAPHIC  CONSTITUENTS  OF  IRON  AND  STEEL  359 


FIG.  60. — Austenite  and  martensite. 


that  it  is  possible  to  distinguish  positively  between  the  two 
constituents,  cementite  and  ferrite. 

To  refer  again  to  the 
diagram  p.  356,  austenite 
is  the  solid  solution  of 
carbon  or  iron  carbide  in 
7-iron,  and  is  the  com- 
ponent that  would  be 
expected  when  a  steel  is 
quenched  as  quickly  as 
possible  from  a  high  tem- 
perature. The  transition 
to  martensite  takes  place 
so  easily,  however,  that 
austenite  is  seldom  formed 
in  the  commercial  hard- 
ening of  plain  carbon 
steels.  It  may  be  ob- 
tained readily  by  quenching  a  steel  containing  manganese  in 
fairly  large  quantities  (10  per  cent  for  example).  Austenite  is 
almost  always  accompanied  by  martensite.  A  characteristic 

photograph  of  the  combi- 
nation is  shown  in  Fig.  60. 
The  unetched  surface  is 
austenite,  and  the  dark  zig- 
zag needles  are  martensite. 

Martensite.  —  This  com- 
ponent represents  the  first 
stage  in  the  decomposition 
of  the  solid  solution.  Pure 
martensite  is  obtained  by 
quenching  small  pieces  of 
steel  at  a  high  tempera- 
ture, and  is  characterized 
by  its  needle-like  structure 
which  becomes  more  strongly 
marked  the  longer  the  etch- 
ing is  continued.  Some  of  the  needles  are  more  strongly  attacked 
than  others,  and  as  a  result  a  marked  roughening  of  the  surface  is 


FIG.  61. — Martensite.     100  X 
(Homerberg.) 


360 


MICROSCOPIC  EXAMINATION  OF  METALS 


FIG.  62. — Martensite  and  troostite. 
100  X-     (Homerberg.) 


produced.  As  shown  in  Fig.  61,  the  needles  intersect  at  about 
60°C.  producing  the  triangular  appearance  which  is  character- 
istic of  the  martensitic  structure.  If  the  cooling  of  the  solid 

solution  takes  place  somewhat 
less  rapidly,  the  second  step 
in  the  decomposition  occurs, 
and  the  martensite  is  found 
associated  with  the  constit- 
uent troostite. 

Troostite. — In  order  to  in- 
dicate the  relation  between 
martensite  and  troostite,  the 
latter  may  be  considered  as 
the  product  of  a  cooling  which 
is  somewhat  slower  than  that 
needed  to  produce  martensite. 
In  commercial  practice,  how- 
ever, troostite  is  almost  always 
formed  by  reheating  (tempering)  quenched  steel  at  a  tempera- 
ture lower  than  400°C.  The  characteristic  properties  of  troostite 
are  the  rapidity  with  which  it  is  colored  by  etching  reagents  and 
the  dark  color  produced. 
Under  the  microscope  it  is 
found,  usually  associated  with 
martensite,  in  the  form  of 
black  irregular  patches  or 
nodules  often  occurring  at 
the  boundaries  of  the  marten- 
site  grains.  The  nearer  the 
temperature  of  reheating  ap- 
proaches 400°C.,  the  greater 
will  be  the  relative  amount  of 
troostite  and  the  softer  the 
material,  as  compared  to  that 
of  martensite,  so  that  by  reg- 
ulating the  temperature  the 
amount  of  troostite,  and  therefore  the  hardness  and  toughness 
of  the  steel,  can  be  altered  within  fairly  wide  limits.  Figures 
62  and  63  illustrate  the  general  appearance  of  troostitic  steel. 


FIG.  63. — Troostite  and  martensite. 
100  X-      (Homerberg.) 


METALLOGRAPHIC  CONSTITUENTS  OF  IRON  AND  STEEL  361 


Sorbite. — One  more  step  in  the  transition  of  the  solid  solution 
from  austenite  to  pearlite  leads  to  the  formation  of  the  material, 
sorbite,  which  may  be  considered  either  as  partially  decomposed 
troostite  or  as  imperfectly 
formed  pearlite.  Its  relation 
to  troostite  may  be  shown  by 
heating  a  specimen  contain- 
ing troostite  to  a  temperature 
between  400  and  600°C.,  and, 
on  the  other  hand,  its  nearness 
to  pearlite  may  be  shown  by 
cooling  the  heated  steel  at 
such  a  rate  that  pearlite  just 
fails  to  be  formed.  The  mi- 
croscopic appearance  of  sor- 
bite  varies  with  its  method  of 

formation,  but  in  general  it       FlG'  «4-a»"*>-    "°  X- 
resembles  the  structure  shown  in  Fig.  64. 

Pearlite. — The  last  stage  in  the  decomposition  of  the  solid 
solution  leads  to  the  formation  of  the  eutectoid  P,  Fig.  59, 
which  because  of  its  resemblance  under  certain  conditions  to 

mother  of  pearl,  has  been 
called  pearlite.  It  consists  of 
alternate  layers  of  ferrite 
(pure  iron)  and  cementite 
which,  after  treatment  with 
the  etching  reagent,  give  to 
the  specimen  a  characteristic 
thumb  print  structure.  The 
microscopic  appearance  of 
pearlite  varies  considerably 
with  the  manner  of  its  forma- 
tion. If  the  steel  is  cooled 
rapidly  through  the  critical 
range,  it  may  have  the  poorly- 
defined  structure  of  sorbitic 
pearlite  but,  with  decreasing  cooling  rate,  the  clearly-marked, 
laminated  structure  becomes  increasingly  evident,  Fig.  65.  An 
abnormal  case  of  decomposed  pearlite  is  illustrated  in  Fig.  66,  an 


FIG.  65. — Pearlite  and  temper  carbon. 
(Fay.) 


362 


MICROSCOPIC  EXAMINATION  OF  METALS 


example  of  what  is  commonly  known  as  spheroidized  cementite. 
When  the  pearlite  is  heated  for  along  time  at  600  to  700°C., 


i. 


»    X*"        stf"    *\  ««^ 

*  **  *         ***          '  ^Jf  -< 


~  -*-  <jr'<*«.  -  *^i^*-«  "*x5r '- .  • 

V>'4      •-     >*"-    ,S^     .7^-'  „  r 


FIG.  66.— Spheroidized  cementite.     100  X.     (Homerberg.) 


365  X 


FIG.  67. — Ferrite. 


1650  X 


the  cementite  which  the  pearlite  contains,  coagulates  into  spher- 
ical masses,  giving  a  steel  which  is  weaker  and  softer  than  the 


METALLOGRAPHIC  CONSTITUENTS  OF  IRON  AND  STEEL  363 


FIG.  68.  —  Pearlite  and  cementite. 
Etched  with  alcoholic  nitric  acid.  100  X- 
(Homerberg.) 


corresponding  pearlite,  but  is  more  ductile  and  has  greater  wear- 
ing qualities. 

Along  the  line  FP  Fig.  59  a  separation  of  pure  iron,  to  which  the 
name  ferrite  has  been  given, 
takes  place.  Pure  ferrite,  seen 
without  the  microscope,  has 
the  appearance  of  a  rough 
surface,  which  the  microscope 
shows  to  be  due  to  the  pres- 
ence of  " etch-figures."  The 
right-half  of  Fig.  67  shows 
the  symmetrical  arrangement 
of  the  etch-figures  on  the  fer- 
rite grains,  produced  in  this 
case  by  etching  with  copper 
ammonium  chloride  (p.  373). 
Associated  with  pearlite,  fer- 
rite is  the  white  structureless 
constituent. 

The  last  of  the  microscopic  constituents  commonly  considered 
is  the  chemical  compound  cementite.     This  substance  separates 

along  the  line  BP,  and  is 
white  and  practically  un- 
affected by  ordinary  etching 
reagents.  It  is  distinguished 
from  ferrite  by  the  fact  that 
it  is  colored  brown  or  black 
by  alkaline  sodium  picrate 
(p.  358).  Figures  68  and  69 
show  the  appearance  of 
cementite  and  pearlite,  the 
first  etched  with  alcoholic 
nitric  acid  and  the  second 
with  Kourbatoff's  reagent. 

The  name  osmondite  is 
sometimes  given  to  that  con- 
stituent which  is  formed  by 
tempering  martensite  at  exactly  400°C.  It  lies  at  the  boundary 
between  sorbite  and  troostite,  and  differs  somewhat  from  each 


FIG.  69.  —  Pearlite  and 
Etched  with  Kourbatoff's 
100  X.  (Homerberg.) 


cementite. 
reagent. 


364 


MICROSCOPIC  EXAMINATION  OF  METALS 


in    its    appearance.     The    name    is   seldom  used  by  American 
met  allographers . 

In  the  iron  range  (above  1.7  per  cent  C.),  the  metallographic 
constituents  which  are  characteristic  are  the  two  forms  of 
graphite  and  the  eutectic.  Primary  graphite  occurs  in  the  form 
of  clusters  of  needles  or  in  long  plates  or  veins.  The  halves  of 
Fig.  70  show  the  two  types  of  graphite  crystals  as  they  occur  in 
different  sorts  of  cast  iron.  Etching  is  not  necessary  to  develop 
the  structure  of  iron  containing  crystalline  graphite. 


FIG.  70. — Graphite  in  iron.     117  X- 

The  second  form  of  carbon  is  that  illustrated  in  Figs.  71  and  72 
showing  the  graphitic  temper  carbon,  which  is  produced  in  the 
manufacture  of  malleable  castings.  Chemically,  it  is  composed 
of  pure  carbon  just  as  crystalline  graphite  is,  but  physically 
it  is  quite  different  in  its  properties  and  appearance.  It  occurs 
most  commonly  in  the  form  of  irregular  black  spots  nearly 
circular  in  form. 

The  eutectic  has  the  thumb  print  structure  shown  in  Fig.  73 
and  is  sometimes  called  ledeburite. 


METALLOGRAPHIC  CONSTITUENTS  OF  IRON  AND  STEEL  365 

In    addition   to   the    normal    constituents    described    above, 
there  are  many  abnormal  components  like  slag,  sulphides  of  iron 


FIG.  71. — Temper  carbon  in  iron.     350  X. 


•  "l 


FIG.  72. — Temper  carbon  in  iron. 

or  manganese  and  the  like.     These  components  are  considered 
in  connection  with  the  particular  classes  of  iron  or  steel  in  which 


366 


MICROSCOPIC  EXAMINATION  OF  METALS 


they  most  commonly  occur.  In  the  chapters  which  follow,  the 
various  classes  of  iron  and  steel  are  discussed  with  special 
reference  to  the  applications  of  the  microscope,  both  as  an  aid  to 
sampling  for  chemical  analysis  and  as  an  additional  means  of 
determining  the  nature  of  a  given  specimen  and  its  suitability 


FIG.  73. — Ledeburite  and  martensite.     350  X- 

for  the  intended  purpose.  It  will  be  impossible,  of  course,  to 
illustrate  many  cases  of  good  and  bad  material,  but  it  is  hoped 
that,  from  the  examples  given,  enough  suggestions  will  be  found 
to  make  the  microscope  of  real  use  to  the  analyst  and  metal 
tester. 


CHAPTER  XXV 
WROUGHT  IRON  AND  STEEL 

Wrought  iron  is  made  by  melting  pig  iron,  as  it  comes  from 
the  smelting  furnace,  with  iron  oxide.  The  resulting  pasty 
mass  is  then  hammered  and  rolled  to  remove  most  of  the  impuri- 
ties. The  carbon  content  is  low,  usually  less  than  0.3  per  cent, 


FIG.  74. — Wrought  iron  made  by  busheling  scrap  iron. 

so  that  the  resulting  iron  consists  chiefly  of  ferrite  with  such 
impurities  (mostly  an  iron  silicate  slag) ,  as  have  not  been  removed 
from  it  by  the  rolling  operation.  Instead  of  making  wrought 
iron  from  pig  iron  and  oxide,  it  is  sometimes  produced  by  heating 
scrap  iron  to  a  semi-pasty  mass  and  then  rolling  it  together. 
Such  a  method  of  manufacture  leads  to  very  great  irregularities 
due  to  the  differences  in  the  scrap  iron,  and  its  character  can  be 

367 


368 


MICROSCOPIC  EXAMINATION  OF  METALS 


determined  by  microscopic  examination  far  more  readily  than 
in  any  other  way,  Fig.  74.  Wrought  iron,  as  commonly  pre- 
pared, is  distinguished  by  the  slag  spots  and  streaks,  which 


FIG.  75. — Slag  in  wrought  iron.     Longitudinal  section.     100  X-     (Homerberg.) 

it  contains,  and  which  make  it  difficult  to  obtain  a  representative 
sample.  Figures  75  and  76  show  the  usual  appearance  of  wrought 
iron,  Fig.  75  showing  the  appearance  of  a  section  made  in  the 


FIG.  76. — Slag  in  wrought  iron.     Transverse  section.     100  X.     (Homcrbcrg.) 

direction  of  rolling  and  Fig.  76,  the  same  specimen  photographed 
at  right  angles  to  the  direction  of  work.  While  the  slag  in  this 
specimen  is  fairly  uniformly  distributed,  it  happens  not  infre- 


WROUGHT  IRON  AND  STEEL 


369 


quently  that  the  distribution  is  very  uneven  as  is  shown  in  Fig. 
77.  If  the  analyst  wishes  to  determine  the  composition  of  the 
slag,  he  can  most  readily  find  its  location  by  the  microscope, 
while  if  he  wants  an  average  sample,  he  will  make  his  sampling 
much  more  representative  through  metallographic  examination 
which  will  show  him  the  distribution  of  the  impurities.  The 
following  table  illustrates  the  marked  differences  that  may  be 
found  in  the  analysis  if  the  sampling  is  not  carried  out  with 
unusual  care. 


FIG.  77. — Slag  inclusions  in  wrought  iron.     350  X. 
TABLE  IV 


Samples  taken 

Phosphorus,  per  cent 

By  planing  over  the  cross-section  

0  17 

By  boring  in  the  dark  spots  

0  30 

Cast  steel  has  been  a  difficult  material  with  which  to  work 
successfully  in  the  past,  but  with  improved  methods  of  melting 
and  temperature  control  its  use  is  constantly  increasing,  especially 
in  the  production  of  small  castings.  The  microscopic  appearance 
of  cast  steel  is  such  as  would  be  predicted  from  the  diagram 
p.  356.  In  the  low-carbon  ranges,  the  surface  shows  a  mixture 

24 


370 


MICROSCOPIC  EXAMINATION  OF  METALS 


FIG.  78. — Cast  steel.     Unannealed. 
100  X-      (Homerberg.) 


of  ferrite  and  pearlite;  at  the  eutectoid  composition,  only  pear- 
lite  is  visible  and,  in  the  high-carbon  cast  steels  (almost  never 

found  in  practice),  cementite 
and  pearlite  are  seen.  The 
microscope  can  be  of  great 
service  in  the  examination 
and  control  of  cast  steel  for 
several  reasons.  In  the  first 
place,  the  castings  are  likely 
to  contain  blow  holes  or  slag 
(oxide)  spots  unless  they  are 
skilfully  melted  and  poured. 
Both  of  these  imperfections 
are  easily  found  on  the  pol- 
ished specimen.  The  most 
serious  imperfection  in  cast 
steel,  however,  results  from 
the  coarse  grained  structure,  which  is  almost  always  found  in 
cast  material,  especially  in  the  low-carbon  steels.  The  grain 
size  of  the  cast  material  can  be  reduced  by  suitable  annealing 
and  this  causes  a  marked  im- 
provement in  the  physical 
properties  of  the  material. 
Figures  78  and  79  show  a  cast 
steel  before  and  after  the  re- 
finement of  its  grain  by  an- 
nealing. While  the  tensile 
strength  is  substantially  the 
same  before  and  after  the 
anneal,  the  ductility  is  more 
than  twice  as  great  in  the 
steel  shown  in  Fig.  79  as  in 
the  coarsegrained,  unannealed 
casting. 

Steel. — The  term  steel  cov- 
ers so  vast  a  range  of  possible  conditions  in  the  alloys  of  iron 
and  carbon  that  anything  like  a  complete  discussion  of  the  many 
varieties  is  a  study  in  itself.1     It  will  be  possible  here  to  con- 
1  See  SAUVEUR,  "Metallography  and  Heat  Treatment  of  Iron  and  Steel." 


PIG.  79. — Cast  steel.     Annealed. 
100   X-     (Homerberg.) 


WROUGHT  IRON  AND  STEEL 


371 


sider  only  those  features  of  the  subject  which  deal  especially  with 
questions  of  sampling  and  with  abnormalities  like  phosphorus 
segregations,  sulphide  inclusions  and  the  like,  which  are  of  special 
interest  to  the  analyst  and  inspector  of  metals. 

Chemical  and  Metallographic  Study  of  the  Solid  Ingot. — If 
samples  are  not  taken  during  the  pouring  as  described  later 
(p.  427)  not  only  is  it  difficult,  expensive  and  time-consuming  to 
get  shavings  from  the  ingot  which  really  represent  the  compo- 
sition of  the  original  charge,  but  in  the  case  of  large  ingots  it  is 
absolutely  impossible. 

Molten  iron  forms  a  solid  solution  with  most  of  the  foreign 
elements  occurring  with  it.  As  regards  the  solidification  it  may 
be  said :  The  solid  solution,  as  it  separates,  is  always  richer  in  the 
constituent  with  the  highest  melting  point  than  is  the  melt 
with  which  the  crystals  are  in  equilibrium;  or,  in  other  words, 
the  melt  retains  more  of  that  constituent  by  means  5 
of  which  the  solidification  temperature  was  lowered 
than  is  present  in  the  crystals  first  formed. 

Now  since  the  temperature  at  which  pure  iron 
solidifies  (1,505°)  is  lowered  by  all  the  impurities  that 
occur  in  technical  iron  as  well  as  by  those  elements 
which  are  added  to  it  intentionally,  it  follows  that 
when  a  large  ingot  solidifies,  the  solid  solu- 
tion that  first  separates  on  the  cold  walls 
of  the  mold  is  freer  from  those  elements 
which  caused  the  lower  melting  point 
(chiefly  carbon,  phosphorus,  sulphur  and 
manganese)  than  that  part  of  the  melt 
which  cools  more  slowly.  These  foreign 
elements,  therefore,  are  forced  continuously 
toward  that  part  of  the  casting  which 
solidifies  last.  In  the  case  of  large  ingots 
this  point  lies  in  the  middle  of  the  ingot  near  its  head  as  indi- 
cated in  Fig.  80.  Segregation,  therefore,  takes  place  during  the 
cooling. 

To  determine  by  chemical  means  the  extent  to  which  segrega- 
tion has  taken  place,  an  ingot  may  be  cut  lengthwise  along  the 
line  S-S  (Fig.  81)  and  borings  taken  at  various  points  of  the  sur- 
face indicated  in  the  drawing  by  cross-hatching.  If  the  results 


FIG.  80. 


s 

FIG.  81. 

372 


MICROSCOPIC  EXAMINATION  OF  METALS 


of  the  analyses  of  samples  taken  from  various  places  on  the 
section  are  plotted  (see  Fig.  82)  it  is  possible  to  get  a  fairly  good 
idea  of  the  distribution  of  the  various  constituents  in  the  ingot. 
It  must  be  remembered  in  this  connection  that  these  analyses 
give  only  the  composition  of  a  few  selected  points  and  that 
their  average  does  not  by  any  means  represent  the  average 
composition  of  the  ingot. 

As  a  rule  segregation  takes  place  to  a  greater  extent  as  the 
quantity  of  elements  other  than  iron  in  the  charge  is  increased. 


Mia 

0.9  0.8  0.7  0.6  0.5  0.4  0.3  0.2  0.1  ( 

die 
0.06        0.10       0.14        0.18       0.22       0.26 

1       I 

• 

==irr^uifnr_ 

\ 

Ca^V'  

^"^^-v^X 

^  

l\ 

\  \ 

V   \ 

/ 

T      ' 
\ 
.       V 

/J\ 

T 
\ 

v_ 

7 

V 

!  ^ 

I 

•  11 

I     ^ 

lr 

lr 

•     / 

^4 

\      2 

Acid  Open-Hearth  Steel 

FIG.  82. 

This  is  shown  clearly  in  the  following  example.1  The  average 
composition  of  an  acid  open-hearth  steel  (samples  taken  from  the 
ladle)  was  0.38  per  cent  carbon,  0.052  per  cent  phosphorus, 
0.52  per  cent  manganese  and  0.061  per  cent  sulfur.  The  ingot 
showed  marked  segregation  as  illustrated  in  Fig.  82.  (The 
analyses  selected  were  from  a  section  taken  through  the  middle 
of  the  ingot.)  The  top  of  the  ingot  was  particularly  rich  in 
phosphorus  and  sulfur  and  there  was  also  a  decided  segregation  of 
carbon. 

The  question  as  to  whether  segregation  exists  or  not  is  of  the 

1  TALBOT,  Iron  and  Steel  Institute,  1905. 


WROUGHT  IRON  AND  STEEL  373 

greatest  practical  importance,  because  the  usefulness  of  the 
material  for  a  definite  purpose  is  often  determined  by  the 
presence  or  absence  of  marked  segregation. 

The  nearer  together  the  points  from  which  the  borings  are 
taken,  the  more  definite  is  the  knowledge  of  the  way  in  which  the 
foreign  elements  are  distributed.  A  purely  chemical  study  like 
the  one  just  described  is  very  time-consuming  and  expensive 
and,  moreover,  the  ingot  must  be  remelted  as  it  is  no  longer 
suitable  for  rolling. 

Macroscopic  Examination  of  Steel. — Under  conditions  of  this 
kind,  the  macroscopic  examination  of  the  specimen  has  been  very 
successful  in  detecting  segregation  in  the  material,  particularly 
the  segregation  of  phosphorus  and  sulfur.  Studies  of  metallic 
surfaces  with  magnifications  of  less  than  ten  diameters  are 
classed  as  macroscopic,  and  the  corresponding  photographs 
(most  commonly  not  magnified  at  all)  are  called  macrographs. 

The  preparation  of  the  surface  for  macroscopic  examination 
requires  somewhat  less  care  than  is  needed  for  the  preparation 
of  a  micro-specimen.  The  following  procedure  will  be  found 
satisfactory  in  most  cases:  First,  plane  or  file  the  surface  until 
it  is  smooth.  Remove  the  marks  of  the  plane  or  file  with  emery 
paper  using  one  or  two  grades  if  needed,  and  finally  finish  with 
fine  emery  powder  or  rouge  on  a  rotating  disk.  With  small 
specimens,  the  sample  can  be  held  against  the  rotating  wheel, 
but  with  large  pieces,  the  disk  should  be  so  arranged  that  it  can 
be  moved  to  any  position  on  the  surface  to  be  polished.  The 
more  perfectly  the  specimen  is  polished,  the  better  defined  will 
be  the  macroscopic  structure,  but  for  many  purposes  polishing 
with  fine  emery  paper  will  be  enough,  without  the  use  of  the  finer 
abrasives. 

Etching  Reagents  for  Macroscopic  Examination. — Three  types 
of  reagents  are  used  for  this  work:  (1)  Quick  acting  solvents,  (2) 
slow  solvents,  (3)  reagents  for  a  special  constituent. 

In  the  first  class  are  concentrated  hydrochloric  acid,  which 
is  not  often  used ;  the  iodide  reagent,  which  is  made  by  dissolving 
10  parts  of  iodine  in  a  solution  of  20  parts  of  potassium  iodide  in 
100  parts  of  water,  and  finally  Heyn's  reagent.  The  last  is  the 
most  useful  of  the  three  and  is  made  by  dissolving  10  parts  of 
the  double  chloride  of  copper  and  ammonium  in  120  parts  of 


374 


MICROSCOPIC  EXAMINATION  OF  METALS 


water.  The  solution  is  allowed  to  stand  for  a  time  after  which 
the  precipitate  is  separated  from  the  solution  by  decantation. 
A  solution  prepared  in  this  way  will  keep  indefinitely. 

The  second  class  is  composed  of  the  dilute  acids.  Sulfuric 
acid  containing  20  c.c.  of  concentrated  acid  in  100  c.c.  of  water 
may  be  taken  as  a  type.  Etching  in  this  case  is  a  slow  process, 

requiring  from  a  few  hours  to  several 
days,  but  the  results  are  excellent. 

The  third  class  of  special  reagents 
includes  those  which  are  used  to 
detect  sulphide  and  phosphide  in- 
clusions, and  their  method  of  applica- 
tion differs  so  much  from  that  usually  adopted  that  they  are 
considered  in  a  separate  section  (cf.  p.  378). 

Reagents  of  the  two  first  classes  are  best  used  by  immersion 
of  the  polished  specimen  as  indicated  in  Figs.  83  and  84.  If 
this  is  not  practicable,  because  of  the  size  of  the  specimen  or  for 
lack  of  a  suitable  container  for  the  reagent,  the  specimen  may  be 
etched  by  swabbing  with  cotton  wool  soaked  in  the  particular 
etching  solution  to  be  used.  The  time  required  to  develop  the 
structure  is  much  longer  under  these  conditions,  and  the  results 
are  not  so  uniform.  Nevertheless,  it  is  quite  possible  to  get 


Section 

FIG.    83. — Etching  dish  with 
section. 


FIG.  84. — Etching  of  large  specimen  for  macroscopic  examination. 

valuable  information  in  this  way.  After  etching  for  the  required 
time,  which  is  usually  from  1  to  5  min.,  wash  the  specimen 
thoroughly  with  running  water,  rinse  with  alcohol  and  finally 
dry  with  a  soft  towel.  Figure  85  shows  a  section  of  a  3-ton  ingot 
polished  as  just  described  and  etched  with  copper  ammonium 
chloride.  This  ingot  was  prepared  by  the  Harmet  process, 
and  will  be  seen  to  be  especially  free  from  segregation.  It  is 


WROUGHT  IRON  AND  STEEL 


375 


not  always  possible  to  divide  a  large  ingot  for  the  purposes  of 

metallographic  examination.     It  cannot  be  done,  for  instance, 

if  the  ingot  is  to  be  rolled  or 

drawn.     If,   in   such   a   case, 

it  is  desirable   to  get  an  ap- 

proximate idea  of  the  distri- 

bution of  foreign  elements  in 

the  ingot,  it  may  be  done,  as 

indicated  in  Fig.  86  by  taking 

a  section  at  the  top  of  the 

ingot,  at  K,  equal  to  about 

one-fourth  of  the  entire  cross- 

section,  a  similar  piece  near 

the  bottom,  at  F,  where  the 

segregation  is  least,   and  ex- 

amining these  specimens  after 

polishing  and  etching. 

Figure  87  shows  the  pol- 
ished section  from  the  top  of 
the  ingot  and  Fig.  88  one 
from  the  bottom  of  an  ingot 
of  basic-Bessemer  steel.  The 
deepest  black  spots  are  due 
to  blow  holes. 

A  circle  of  large  holes  sepa- 
rates the  inner  from  the 
outer  zone  in  both  sections. 
The  core  is  darker  in  both 
cases  than  the  outer  edge.  In 
this  inner  zone  are  found 
larger  or  smaller  spots  rich 
in  phosphorus.  A  dark  color 
after  etching  with  copper 
ammonium  chloride  is  gen- 
erally an  indication  of  a  high 
phosphorus  content.  The 
other  impurities,  however, 
particularly  the  oxide  and 

,  ~  ,  FIG.  85.  —  Etched  section  from  a  3-ton 

sulnde    compounds,    tend    to  ingot. 


376 


MICROSCOPIC  EXAMINATION  OF  METALS 


K 


collect  at  those  places  where  the  phosphorus  content  is  greatest, 
so  that  in  case  the  color  is  unusually  dark  it  is  safe  to  assume 
that  the  sulfide  and  oxide  content  is  also  high.1 

It  will  be  noticed  that  at  the  top  of  the  ingot  the  boundary 
between  the  inner  and  outer  zones  is  sharply  marked  by  a  dark 
;  band,  while  at  the  lower  end  (Fig.  88)  there  is  a 

gradual  transition  without  any  sharply  marked, 
dividing  line.  The  dark  color  in  the  inner  zone  of 
section,  F,  from  the  foot  of  the  ingot,  is  very  slight 
as  compared  to  that  of  the  corresponding  part  of 
the  upper  section,  K.  The  conclusion  may  be 
drawn  from  these  facts  that  there  is  a  marked 
difference  in  the  percentage  of  impurities  at  the 
top  and  at  the  bottom  of  the  ingot.  This  opinion 
is  confirmed  by  analyses  made  from  different  parts 
of  the  ingot. 

The  macroscopic  examination  (etching  test) 
gives,  therefore,  a  satisfactory  idea  of  the  distri- 
bution of  foreign  matter  in  the  material.  It  shows 
whether  zone-formation  due  to  segregation  has 
occurred,  the  boundaries  between  the  different 
zones,  and  gives  a  means  of  determining  the  most 
suitable  places  for  taking  samples  for  chemical  and 
mechanical  tests. 

Two  methods  of  recording  the  macroscopic  struc- 
ture of  a  steel  without  the  use  of  the  photographic 
plate  have  been  devised,  the  first  the  direct  sulfur  print  on  silk 
or  on  photographic  paper  and  the  second  a  print  made  by  the  use 

TABLE  V 


FIG. 


From  top  of  ingot 

From  bottom  of  ingot 

Inside, 
per  cent 

Outside, 
per  cent 

Inside, 
per  cent 

Outside, 
per  cent 

Carbon             

0.11 

0.52 
0.15 

0.06 
0.48 
0.07 

0.07 
0.47 
0.08 

0.07 
0.46 
0.05 

Manganese              

Phosphorus                       

1  In  case  of  doubt,  microscopic  examination  and  the  sulfur  print  (p.  378) 
will  confirm  or  disprove  the  presence  of  these  constituents. 


WROUGHT  IRON  AND  STEEL 


FIG.  87. — Section  K  from  the  top  of  the  ingot. 


t!h: 


M 


378  MICROSCOPIC  EXAMINATION  OF  METALS 

of  printer's  ink  on  the  etched  surface.     Both  of  these  operations 
come  under  the  third  class  of  macroscopic  etching  methods. 

Sulfur  printing  depends  on  the  fact  that  sulfur  exists  in 
the  steel  either  as  iron  sulfide  or,  more  commonly,  manganese 
sulfide,  both  of  which  are  readily  decomposed  by  dilute  acids 
with  the  evolution  of  hydrogen  sulfide.  In  the  older  method 
of  Heyn  and  Bauer,  the  polished  surface  was  covered  with  a 
piece  of  white  silk  which  was  then  moistened  with  a  solution  of 
the  following  composition: 

10  g.  mercuric  chloride 

20  c.c.  hydrochloric  acid  (d.  1.12) 

100  c.c.  water. 

Wherever   sulfide   inclusions   are   present,   hydrogen   sulfide   is 
evolved,  and  will  cause  the  deposition  of  black  mercuric  sulfide. 

The  action  should  be 
allowed  to  continue  for 
4  or  5  min.  The  ap- 
pearance of  sulfur  prints 
made  in  this  way  is 
shown  in  Figs.  89  and 
90  in  which  the  dark 
streaks  and  spots  corre- 
spond to  the  sulfide  in- 
clusions in  the  sample. 

Silk  printing  has  been 
replaced  to  a  consider- 
able extent  in  American 
practice  by  a  modifica- 
tion of  the  process  sug- 
FIG.  89.— Sulfur  print  on  silk.  gested  by  B  a  u  m  a  n  n. 

Velox,     Cyko    or    other 

developing  paper  is  soaked  in  dilute  acid  (sulfuric  or  hydrochloric 
acid  having  a  concentration  of  from  2  to  10  per  cent),  held  on  the 
polished  specimen  for  about  20  sec.,  washed  in  water  and  then 
fixed  in  "acid  hypo"  in  the  usual  way.  Sulfide  inclusions  are 
again  indicated  by  black  spots  due,  in  this  case,  to  the  reaction 
of  the  evolved  hydrogen  sulfide  with  the  silver  of  the  paper. 
Prints  with  printer's  ink  illustrate  in  a  striking  fashion  the 


WROUGHT  IRON  AND  STEEL 


379 


i 


•I 


380  MICROSCOPIC  EXAMINATION  OF  METALS 

larger  surface  features  of  the  polished  specimen.  The  method 
has  been  used  for  many  years  but  until  recently  has  been  difficult 
to  control.  Humfrey1  has  developed  an  etching  method  which 
makes  it  possible  to  produce  excellent  direct  prints  from  samples 
having  the  comparatively  rough  surface  given  by  an  emery  paper 
finish.  The  reagents  used  are  neutral  copper  ammonium 
chloride,  120  g.  per  liter  and: 

Copper  ammonium  chloride 120  g. 

Hydrochloric  acid  (cone.) 50  c.c. 

Water 1,000  c.c. 

The  exact  proportion  of  HC1  varies  somewhat  with  different  steels 
and  must  be  determined  by  trial. 

Start  the  etching  with  the  neutral  solution  of  the  copper  salt 
and  continue  with  this  reagent  until  the  scratches  left  by  the 
emery  paper  have  been  eaten  away.  Determine  this  point  by 
wiping  off  the  copper  deposit  and  examining  the  dried  surface. 
When  the  scratches  have  disappeared,  start  the  etching  again 
with  enough  of  the  neutral  reagent  to  form  a  complete  but  thin 
covering  of  .flocculent  copper.  Then,  in  successive  applications, 
increase  the  acidity  of  the  solution  to  its  maximum.  Continue 
the  treatment  with  the  acid  reagent  for  about  15  min.  Wipe 
off  the  deposited  copper  and  rub  the  matt  surface  lightly  to 
bring  out  the  relief  portions  in  strong  contrast.  The  total  time 
taken  for  the  preparation  of  the  specimen  is  from  20  min.  to  1  hr. 

Printing. — The  most  perfect  reproductions  of  the  etched  sur- 
face are  made  by  the  regular  book  printing  process,  but  very 
satisfactory  results  may  be  obtained  by  inking  the  surface  of  the 
etched  specimen  by  means  of  a  roller  of  the  type  used  in  the 
mimeograph,  after  which  the  impression  is  taken  by  pressing  a 
sheet  of  glossy  printing  paper  against  the  inked  surface  by 
means  of  a  letter-copying  press  or  similar  device.  This  method 
has  been  used  with  great  success  not  only  in  the  study  of  ingots 
but  also  with  forged  or  otherwise  worked  material. 

Defective  areas  in  the  original  ingot  should  be  removed  from 
the  ingot  before  the  steel  is  used  for  rolling,  shaping  or  any  one  of 

1  J.  C.  W.  HUMFREY,  Macro-etching  and  macro-printing,  J.  Iron  and 
Steel  Inst.,  99  (1919)  273. 


WROUGHT  IRON  AND  STEEL 


381 


the  numerous  operations  to  which  it  might  be  subjected  as  it  is 
found  that  imperfections  in  the  structure  of  the  ingot  are  almost 
invariably  carried  into  the  finished  product.  Here,  as  in  the  case 
of  the  ingot  itself,  the  macroscopic  examination  is  of  the  utmost 
value  in  the  inspection  of  the  material.  A  few  examples  will 
illustrate  the  application  of  the  physical  method  of  testing  as  an 


FIG.  91. — From  the  top  of  the  ingot.       FIG.  92. — From  the  base  of  the  ingot. 

aid  to  the  chemist  not  only  in  selecting  his  samples  but  also  in 
forming  an  opinion  as  to  the  character  of  the  material  under 
examination. 

Segregation  in  wrought  iron  and  steel  cannot  be  wholly  over- 
come though  with  suitable  precautions  it  can  be  greatly  reduced. 


382  MICROSCOPIC  EXAMINATION  OF  METALS 

It  is  important,  therefore,  for  the  steel  mill  to  have  a  means  of 
determining  from  time  to  time  the  amount  of  segregation  in  the 
ingots.  To  cut  sections  from  the  ingot  itself  for  the  purpose  of 
making  microscopical  tests  would  be  difficult  and  would  interfere 
seriously  with  mill  operations.  An  examination  of  pieces  rolled 
from  the  top  and  from  the  bottom  of  the  ingot  answers  the 
purpose. 

If  an  ingot  containing  segregated  material  is  rolled  into  any 
particular  shape  (angle-iron,  beam,  rail,  plate,  etc.)  the  zone  of 
segregation  appears  in  the  rolled  piece.  The  I-beams  shown  in 
Figs.  91  and  92  are  rolled  from  the  same  basic-Bessemer  ingot  from 


FIG.  93. — From  the  top  of  the  ingot.     FIG.  94. — From  the  base  of  the  ingot. 

which  the  sections  shown  in  Figs.  87  and  88  were  taken.  Figure 
91  corresponds  to  the  top  of  the  ingot  and  Fig.  92  to  the  bottom. 
In  the  beam  rolled  from  the  top  of  the  ingot  the  dark  dividing 
band  between  the  inner  and  outer  zones  is  clearly  marked  while 
in  the  other  beam  no  division  is  evident.  The  blow  holes  have 
disappeared.  The  agreement  between  the  original  ingot  and 
the  rolled  material  with  respect  to  zone  formation  is  clearly 
shown. 

Figures  93  and  94  are  made  from  basic-Bessemer  ingot 
rolled  out  to  small  rods.  Figure  93  represents  in  this  case 
the  top  of  the  ingot,  while  Fig.  94  is  from  the  lower  end. 
The  segregation  phenomena  are  exactly  similar  to  those  just 
described. 


WROUGHT  IRON  AND  STEEL 
TABLE  VI 


383 


Corresponding  to  top  of  ingot 

Corresponding  to  bottom  of  ingot 

Center, 
per  cent 

Edge, 
per  cent 

Center, 
per  cent 

Edge, 
per  cent 

Carbon  

0.110 
0.520 
1.125 

0.08 
0.50 
0.08 

0.090 
0.480 
0.075 

0.09 
0.52 
0.08 

Manganese  
Phosphorus  

Here  again  the  differences  between  the  center  and  the  edge 
of  the  piece  rolled  from  the  top  of  the  ingot  are  considerable, 
while  these  differences  almost  disappear  in  the  other  pieces 


FIG.  95. — Section  of  a  connecting-rod  screw. 

These  examples  indicate  that  in  order  to  get  an  idea  of  the 
nature  of  the  segregation  in  the  ingot,  it  is  not  enough  to  take 
a  section  from  a  piece  rolled  from  one  end  of  the  ingot,  but  it  is 
absolutely  necessary  to  have  sections  corresponding  to  both 
ends,  and  in  many  cases  to  have  a  section  representing  the  center 
of  the  ingot  as  well. 


384 


MICROSCOPIC  EXAMINATION  OF  METALS 


Figure  95  shows  the  etched  surface  of  a  broken  connecting- 
rod.  The  inner  core  K  contains  numerous  dark  spots  rich  in 
small,  non-metallic  inclusions.  The  bright  outer  zone  is  crossed 
by  dark  lines  perpendicular  to  the  sides  of  the  quadrangle 
which  bounds  the  inner  zone.  These  come  from  the  blow  holes 
which  were  perpendicular  to  the  edges  of  the  original  ingot  and 
were  closed  up  during  the  rolling.  The  four-cornered  cross-sec- 
tion of  the  inner  zone  shows  that  the  ingot  from  which  the  rod  was 
made  was  quadrangular  in  cross-section. 

Analyses  gave  these  values: 

TABLE  VII 


Inner  zone, 
per  cent 

Outer  zone, 
per  cent 

Carbon 

0  11 

0  09 

Phosphorus  
Sulfur 

0.08 
0  08 

0.05 
0  04 

Manganese 

0  72 

0  70 

Silicon  

Trace 

Trace 

Copper 

0.02 

0  02 

Nickel  '  

0.07 

0.07 

FIG.  96. — Square  bar  of  basic-Bessemer  steel. 

Carbon,  phosphorus   and   sulfur  have  segregated  in  the  inner 
zone. 


WROUGHT  IRON  AND  STEEL 


385 


Figure  96  is  the  polished  cross-section  of  a  square  bar  of 
basic-Bessemer  steel.  The  section  shows  in  the  dark  colored 
inner  zone  numerous  small  non-metallic  inclusions  evidently 
of  a  sulfidic  character.  Analyses  of  the  two  zones  gave: 


TABLE  VIII 


Inner  zone, 
per  cent 

Outer  zone, 
per  cent 

Carbon 

0  092 

0  096 

Manganese  

0  410 

0  380 

Silicon 

0  012 

0  014 

Phosphorus  

0  060 

0  050 

Sulfur.                    

0  072 

0  030 

Copper  

0  074 

0  050 

Nitrogen  

0  010 

0  009 

Besides  the  slight  segregation  of  phosphorus  there  is  a  much  larger 
sulfur  segregation  in  the  inner  zone. 

If,  in  the  cases  just  cited,  the  samples  for  analysis  had  not 
been  taken  by  planing  across  the  entire  section  p.  423,  but  by 
boring,  it  would  have  been  quite  possible  to  obtain  unreliable 
results  even  if  holes  had  been  drilled  all  the  way  through  the 
metal.  If,  for  example,  a  round  rod  is  drilled  as  indicated  by 
7,  Fig.  97  the  drillings  do  not  correspond  to  the  average  compo- 
sition as  would  those  made  by  planing.  The 
relative  position  of  the  holes  has  an  in- 
fluence on  the  values  obtained.  (See  points 
7  and  77  in  Fig.  97.)  More  drillings  from 
the  unsegregated  outer  zone  would  be  made 
by  a  hole  at  7  than  at  77.  The  drillings 
from  hole  7  are  therefore  poorer  in  phos- 
phorus and  sulfur  than  those  from  hole  77. 

These  facts  hold  not  only  for  round  or 
square  pieces,  but  also  for  those  of  any  other  shape  if  seg- 
regation into  any  inner  and  outer  zone  has  taken  place  in  the 
ingot. 

Even  with  correct  sampling,  analytical  differences  may  occur 


FIG.  97. 


25 


386 


MICROSCOPIC  EXAMINATION  OF  METALS 


under  certain  conditions.  Assume,  for  example,  that  the 
material  of  which  the  bar  or  other  piece  consists  was  sampled 
correctly  by  the  shipper  by  planing  over  the  whole  cross-section 
and  a  phosphorus  determination  made.  The  sample  contained 
"  a  "  per  cent  phosphorus.  The  rod  was  then  turned  down  by  the 
purchaser  and  used  for  construction  work.  Because  of  a  break, 
the  finished  product  was  analyzed  for  phosphorus.  In  this  case 
too  the  sample  was  taken  correctly  by  planing.  The  average 
phosphorus  content  would  have  been  greater  in  this  case  if  the 
original  bar  contained  a  core  rich  in  phosphorus,  as  the  outer 
zone,  low  in  phosphorus,  would  have  been  removed  by  turning. 
Microscopic  tests  would  indicate  the  difference  between  the 
original  bar  and  the  finished  product. 

As  stated  on  p.  381  and  illustrated  in  Fig. 
91,  the  segregation  zone  goes  through  the 
various  processes  of  mechanical  treatment, 
rolling,  forging,  etc.,  without  coming  to  the 
surface  of  the  piece.  Because  of  the  flowing 
of  the  material  of  the  outer  zone  on  rolling, 
very  considerable  changes  in  the  relative 
areas  and  shapes  of  the  inner  and  outer 
zones  may  take  place.  The  dark  inner  zone 
forms  a  much  larger  proportion  of  the  total 
area  in  the  web  of  the  I-beam  (Fig.  91)  than 
in  the  flanges.  The  same  thing  is  true  in  the  case  of  rails  and 
other  rolled  forms.  Figure  98  is  a  drawing  of  an  etched  rail 
section.  The  inner  zone  is  cross-hatched.  The  ratio  between 
the  areas  of  the  inner  and  outer  zones  in  the  different  parts  of 
the  rail  were  as  follows: 


Head 


Foot 


FIG. 


TABLE  IX 


Proportional  area 
of  inner  zone,  K, 
per  cent 

Proportional  area 
of  outer  zone,  R, 
per  cent 

In  head  of  rail                                 

32.1 

67.9 

In  web  of  rail                                         

63.4 

36.6 

In  foot  of  rail  .  . 

14.4 

85.6 

WROUGHT  IRON  AND  STEEL 
Chemical  analysis  gave  the  following  results: 

TABLE  X 


387 


Inner  zone  K, 
per  cent 

Outer  zone  R, 
per  cent 

Phosphorus  

0.127 

0  063 

Sulfur                                      .    .                 

0  060 

0  023 

Manganese 

0  550 

0  500 

The  differences  in  chemical  composition  between  the  inner  zone 
K  and  the  outer  zone  R  are  quite  marked.     A  representative 


FIG.  99. — Cross-section  of  a  mine  rail. 

sample  for  analysis  can  be  obtained  only  by  planing  over  the 
entire  cross-section.  Planing  part  of  the  section  (for  example 
only  the  upper  half)  would  give  incorrect  values  because  of  the 
uneven  distribution  of  the  sulfur  and  phosphorus  in  the  final 
product.  (See  Table  IX.) 


388 


MICROSCOPIC  EXAMINATION  OF  METALS 


A  similar  case  of  marked  segregation  is  illustrated  in  Fig.  99 
the  cross-section  of  a  mine  rail.  Three  distinct  zones  are 
noticeable. 

(a)  A  narrow  rim  around  the  outer  edge  of  the  section,  colored 
dark  by  the  etching  reagent. 

(6)  An  intermediate  zone  #2  which  stays  bright  after  etching. 

(c)  An  inner  zone  made  very  dark  by  etching  and  containing 
many  small,  non-metallic  inclusions,  probably  due  to  deoxidation. 

Chemical  analysis  gave: 

TABLE  XI 


Inner  zone,  K, 
per  cent 

Outer  zones,  R  \  and 
J?2,  per  cent 

Phosphorus 

0    158 

0  115 

Sulfur  

0.064 

0.042 

Owing  to  the  peculiar  distribution  of  the  zones  which  are  rich 
in  phosphorus,  the  average  phosphorus  content  in  the  two  outer 
zones  Ri  +  R2  is  also  high. 

Sheet  iron,  boiler  plate,  hoop  iron  and  other  flat  forms  often 
give  difficulty  in  sampling  as  the  following  example  illustrates. 
A  red-short  boiler  plate  was  analyzed  for  sulfur  by  several 
chemists.  Samples  of  the  steel  were  sent  in  sealed  packages 

to  the  various  laboratories,  and 
the  results  returned  varied  from 
0.067  per  cent,  to  0.24  per  cent 
sulfur.  The  differences  were 
altogether  greater  than  possible 
differences  due  to  different  meth- 
ods of  analysis  or  to  experimental 

FIG.  100.— Red  short  boiler  plate.        errors 

Metallographic  study  explained  the  situation  at  once,  showing 
not  only  the  reasons  for  the  analytical  differences  but  also  the 
cause  of  the  original  difficulty  with  the  boiler.  Marked  zone 
formation  had  taken  place  due  to  segregation  as  shown  in  Fig. 
100.  After  the  segregated  areas  had  been  located,  borings  were 
taken  from  the  different  zones  and  gave  on  analysis  the  following 
sulfur  values. 


WROUGHT  IRON  AND  STEEL  389 

Sample  Sulfur, 

taken  from  per  cent 

Zone  / 0.067 

Zone// 0.201 

Zone  III 0.240 

The  samples  submitted  to  the  different  laboratories  were  evi- 
dently incorrectly  taken  by  drilling  or  planing  in  different  places 
so  that  one  laboratory  had  samples  from  the  low  sulfur  zone  7, 
the  second  from  the  area  II,  which  was  somewhat  richer  in  sulfur, 
and  a  third  from  the  most  segregated  area  III.  An  average 
value  could  be  obtained  only  by  planing  over  the  entire  cross- 
section  of  the  specimen  and  even  then  the  macroscopic  results 
would  be  of  greater  value  than  those  obtained  by  analysis. 

Many  more  examples  of  segregation  in  rolled  or  shaped  material 
might  be  cited  but  the  illustrations  given  will  serve  to  indicate 
the  usefulness  of  macroscopic  study,  both  as  an  aid  in  getting 
samples  which  are  actually  representative  of  the  material  under 
inspection  and  as  a  means  of  getting  independently  of  chemical 
analysis  or  physical  testing,  extremely  useful  information  con- 
cerning the  properties  of  the  metal. 

Before  the  subject  of  steel  ingots  and  the  rolled  or  wrought  ma- 
terial made  from  them  is  left,  a  brief  reference  to  Stead's  reagent 
must  be  made.  This  reagent  is  used  for  the  purpose  of  detecting 
phosphorus  segregations  in  steel  and  is  prepared  as  follows : 

Cupric  chloride 10  g. 

Magnesium  chloride 40  g. 

Hydrochloric  acid 20  c.c. 

Alcohol,  sufficient  to  make 1,000  c.c. 

Cover  the  specimen  with  a  thin  layer  of  the  reagent,  but  do  not 
immerse  it.  Shake  off  the  layer  of  liquid  after  it  has  acted  for  1 
min.,  and  replace  it  with  a  fresh  portion  of  the  acid  mixture. 
Repeat  the  operation  until  the  desired  results  have  been  obtained, 
then  wash  first  with  boiling  water  and  finally  with  alcohol. 
Copper  deposits  on  the  phosphorus-free  areas  first,  and  by 
successive  treatments  it  is  possible  to  determine  with  a  consider- 
able degree  of  accuracy  the  relative  phosphorus  concentrations 
in  different  areas  of  the  specimen.  If  the  phosphorus  is  highly 
localized  at  any  point,  the  segregated  spots  will  stay  bright  even 
after  ten  treatments  with  the  etching  material. 


CHAPTER  XXVI 
GENERAL  STUDY  OF  STEEL  WITH  THE  MICROSCOPE 

The  general  features  of  the  steel  specimen,  segregation  of 
phosphorus,  sulfide  inclusions  and  the  like  may  be  studied  without 
the  use  of  the  microscope,  but  the  exceedingly  important  changes 
due  to  tempering,  annealing  and  other  operations,  included 
under  the  general  head  of  heat  treatment,  can  be  followed 
only  with  the  microscope.  A  complete  review  of  all  the  changes 
produced  by  varying  the  rates  of  heating  and  cooling  and  the 
microscopic  appearances  of  the  resulting  steels,  would  cover 
almost  the  whole  field  of  steel  metallography.  Therefore  it 
will  be  possible  to  select  only  a  limited  number  of  examples  to 
show  the  ways  in  which  the  microscope  may  be  used  to  aid  the 
chemist  in  his  professional  work. 

Tempering. — Tempering  is  the  term  used  to  indicate  the 
softening  of  hardened  steel  (martensite  or  austenite,  p.  357) 
by  reheating  at  suitable  temperatures.  The  higher  the  reheating 
temperature,  the  softer  is  the  material  due  to  the  change  from 
martensite  to  troostite  and  finally  to  sorbite.  In  the  lower 
ranges  of  tempering,  the  microscope  shows  the  gradual  increase 
in  the  amount  of  troostite  and  when  the  temperature  reaches 
400°C.  the  change  to  troostite  should  be  complete.  From  400 
to  600°C.  sorbite  in  increasing  amounts  should  be  found.  Since 
the  properties  of  the  two  constituents  differ  so  materially,  the 
microscope  makes  it  possible  to  determine  much  more  accurately 
than  could  be  done  by  chemical  analysis,  whether  or  not  the 
material  has  been  treated  to  give  the  properties  necessary  for 
the  purpose  for  which  it  is  to  be  used. 

Annealing. — Steel  is  annealed  in  order  to  relieve  strains  pro- 
duced by  sudden  chilling  or  by  working,  or  it  may  be  done  with 
the  idea  of  refining  a  steel  in  which  the  crystal  grains  are  too 
large  to  give  to  the  material  its  best  physical  properties.  In 
order  that  annealing  may  be  effective,  the  material  must  be 
heated  above  its  critical  range.  If  it  has  not  been  so  heated  the 
microscope  will  show  crystal  grains  of  the  same  size  as  before 

390 


GENERAL  STUDY  0$  STEEL  WITH  THE  MICROSCOPE       391 

the  annealing  operation.  The  greatest  dangers  in  annealing, 
however,  and  the  two  conditions  most  readily  detected  are 
overheating  and  burning.  The  former  occurs  when  the  an- 


A  B 

FIG.   101. — A  shows  overheated  steel  and  B  fine  grained  structure. 

nealing  operation  is  carried  out  at  too  high  a  temperature,  and 
leads  to  an  abnormal  growth  of  the  crystal  grains  and  a  conse- 


A  =  100  x  B  =  300  x 

FIG.   102. — Burned  low  carbon  steel.     (Johnson.) 

quent  weakening  of  the  material.  The  microscopic  appearance 
of  an  overheated  steel  in  contrast  to  a  properly  annealed  steel 
is  shown  in  Fig.  101.  A  shows  the  very  coarse  structure 


392 


MICROSCOPIC  EXAMINATION  OF  METALS 


FIG.  103. — Sulfide  inclusions. 


characteristic  of  overheated  steel,  while  B  shows  the  fine  grained 
structure  of  good  steel.  Burning,  a  much  more  serious  defect, 
is  caused  by  raising,  the  annealing  temperature  almost  to  the 

fusion  point  of  the  metal 
(above  FeB,  Fig.  59,  p. 
356).  It  causes  a  marked 
increase  in  the  size  of 
the  grains,  but  in  addi- 
tion, as  will  be  seen  in 
Fig.  102,  there  is  a 
marked  thickening  and 
darkening  of  the  grain 
boundaries.  This  may 
be  due  to  an  escape  of 
dissolved  gases,  to  oxide 
formation  or  to  segre- 
gations of  molten  phos- 
phide. In  the  latter  case 
the  burned  structure  is 
most  clearly  developed  by  the  use  of  Stead's  phosphide  reagent 
(p.  389). 

Other  applications  of  the  microscope  to  the  general  study 
of  steel  are  common.  Slag  or 
sulphide  inclusions,  Fig.  103, 
too  small  to  be  detected  by 
macroscopic  examination  be- 
come evident,  irregular  distri- 
bution of  troostite,  martensite 
and  sorbite  areas  due  to  un- 
even tempering,  Fig.  104,  may 
be  detected  and  in  many  other 
similar  cases  the  microscope 
will  be  found  of  great  value 
in  the  study  of  suspected 
material. 

Cold  -  worked    Material.  — 
Mechanical  work,  such  as  roll- 
ing, forging  or  pressing  which  is  done  above  the  critical  tempera- 
ture, Fig.  59,  p.  356  (about  700  to  850°C.)  produces  changes  in  the 


FIG.     104. — Sorbite,    martensite    and 
troostite.     100  X.     (Homerberg.') 


GENERAL  STUDY  OF  STEEL  WITH  THE  MICROSCOPE       393 

shape  of  the  material,  but  any  changes  in  the  internal  structure 
of  the  metal  will  be  more  or  less  completely  overcome  during 
the  cooling  through  the  critical  range,  especially  if  the  rate  of 
cooling  is  slow,  as  is  commonly  the  case.  The  chief  advantage 
of  the  microscope  in  the  case  of  such  " hot- worked"  material  is 
in  determining  the  size  of  the  crystal  grains  and  therefore  in 
forming  an  estimate  of  the  finishing  temperature  (that  tempera- 
ture at  which  working  stops).  Jt  is  generally  true  that  the 
higher  the  finishing  temperature  above  the  critical  temperature, 
the  coarser  and  therefore  the  less  satisfactory  will  be  the  resulting 


FIG.   105.— Cold  drawn  steel.     100  X.     (Homerberg.) 


structure.  If  the  work  is  carried  on  at  temperatures  lower 
than  about  700°C.,  and  especially  if  the  material  is  rolled  or 
drawn  at  ordinary  temperatures,  the  operation  is  known  as 
"cold  working."  Such  material  is  always  found  in  a  more  or 
less  strained  condition.  Cold  work  may  be  done  intentionally, 
or  it  maybe  done  by  accident  if  the  operations  of  rolling,  drawing 
and  the  like  are  not  stopped  above  the  critical  range.  In  either 
case  the  microscope  may  be  used  to  great  advantage,  as  indi- 
cated in  the  photograph,  Fig.  105,  which  illustrates  a  piece  of 
steel  subjected  to  severe  strain  in  the  cold  condition.  The 
distribution  of  the  crystal  grains  in  lines  parallel  to  the  direction 
of  the  pull  is  plainly  evident.  The  material  has  a  somewhat 


394 


MICROSCOPIC  EXAMINATION  OF  METALS 


higher  tensile  strength  than  unstrained  steel  but  a  greatly 
decreased  ductility  and  is  especially  liable  to  fracture  when  it  is 
subjected  to  sudden  shock.  The  condition 
of  " strain  hardness"  (see  p.  458)  may  be 
relieved  by  suitable  annealing.  If  the 
strain  hardness  has  been  wholly  removed, 
the  steel  should  show  regularly  formed  crys- 
tals with  no  evidence  of  elongated  grains 
so  that  by  observing  the  extent  to  which 
the  distorted  grains  have  been  restored  to 
their  normal  shape  and  size,  the  effective- 
ness of  the  annealing  may  be  determined. 
Strain  hardening  is  often  produced  unin- 
tentionally in  various  ways,  as  for  example, 
in  the  hammering  of  rivets  after  they  have 
become  too  cold  to  allow  for  the  readjustment  of  the  crystal  shape 
after  the  distortion  of  rivetting.  It  is  often  necessary  to  force  the 
steel  parts  of  a  building  or  bridge  into  place  by  the  use  of  the 


FIG.  106. 


FIG.   107. — Steel  under  tension.     (A  in 
Fig.   106.)      (Homerberg.) 


FIG.    108.  —  Steel   under    compression. 
(B  in  Fig.  106.)      (Homerberfj.) 


sledge  hammer.  In  such  cases  cold  work  is  done,  and  may  be  the 
cause  of  brittleness  leading  to  serious  consequences  later.  Diffi- 
culties of  this  sort  could  not  be  controlled  by  microscopic  exami- 
nation, but  if  accidents  occur  under  similar  conditions  it  is  often 
possible  to  determine  the  cause  much  more  surely  by  the  micro- 


GENERAL  STUDY  OF  STEEL  WITH  THE  MICROSCOPE      395 


scope  than  in  any  other  way.  Figures  107  and  108  are  photo- 
graphs taken  at  the  points  A  and  B  of  the  bent  steel  rod  indicated 
in  the  sketch,  Fig.  106.  A  illustrates  the  effect  of  tension  while 
B  shows  the  results  of  cold  compression.  Such  distorted  mate- 
rial is  often  found  at  the  edge  of  a  punched  rivet  hole,  and  not 
infrequently  the  resulting  brittleness  is  great  enough  to  cause 
cracking  of  the  material. 

Case-hardened  Material. — It  is  often  necessary  to  treat  a 
piece  of  steel  in  such  a  way  that  a  hard  outer  layer  will  be  formed 
around  a  soft  core.  This  operation  of  case-hardening  produces 
a  layer  effect,  which  makes  the  question  of  adequate  sampling 
a  most  difficult  one.  The  outer  case  which  is  much  richer  in 
carbon  than  the  core  may  have  a  thickness  of  several  milli- 
meters, and  if  the  material  has  been  quenched,  as  is  often  the 
case,  it  will  be  extremely  hard.  If  such  a  piece  is  to  be  analyzed, 
it  must  first  be  annealed  in  order  to  get  any  sample  at  all.  Spe- 
cial care  must  be  taken  to  prevent  surface  oxidation  during  the 
annealing  with  a  consequent  loss  of  carbon.  The  annealing 
time,  therefore,  is  made  as  short  as  possible  (about  J£  hr.),  and 
the  annealing  temperature  is  also  kept  as  low  as  possible  (750  to 
800°C.).  If  the  specimen  in  question 
is  ordinary  carbon  steel  it  may  be 
quenched  in  water  after  the  furnace 
temperature  has  fallen  below  700°  as 
hardening  does  not  take  place  below 
the  pearlite  point. 

If  the  annealing  furnace  is  kept  at  a 
high  temperature  (1,000°  or  higher) 
and    the    time   is   unduly   prolonged 
(several  hours  for  example)  a  marked 
diffusion  of  the  carbon  into  the  low- 
carbon  area  takes  place.     The  chem- 
ical  and   microscopical  study  then  gives  a  wrong  idea  of  the 
original  distribution  of  the  carbon  in  the  sample.     The  follow- 
ing illustration  shows  how  great  this  change  can  be. 

Arnold  and  M.  Williams1  fitted  a  piece  of  steel  with  1.78  per 
cent  carbon  into  a  cylinder  of  iron  nearly  free  from  carbon  and 
heated  10  hr.  in  a  vacuum  at  1,000°.  Figure  109  shows  the 

1  J.  Iron  and  Steel  Institute,  1899,  85. 


FIG.  109. 


396 


MICROSCOPIC  EXAMINATION  OF  METALS 


distribution  of  the  carbon  after  the  heating.  The  dark  inner  part 
is  the  steel  core  and  the  outer  part  the  iron  shell.  The  circles 
represent  the  different  layers  which  were  removed  successively 
and  analyzed  for  carbon.  The  inscribed  percentages  show  clearly 
the  gradual  diffusion  of  the  carbon  from  the  steel  to  the  soft  iron. 
Metallographic  examination  shows  with  great  sharpness  the 

depth  of  the  carbonized  layer  and 
gives  at  least  an  approximate  idea 
of  the  increase  in  carbon  content. 

Figure  llO  shows  with  fourfold 
magnification  the  cross-section  of  a 
small  case-hardened  axle-bearing. 
The  thickness  of  the  carbon-rich 
layer  R  (light  in  the  photograph) 
was  about  0.55  mm.  The  outer  zone 
R  contained  0.95  per  cent  carbon 
while  the  core  K  (dark  in  the  photo- 
graph) had  only  about  0.1  per 
cent.  There  was  a  fairly  sharp 
transition  from  the  high-carbon 
content  of  zone  R  to  the  low- 
carbon  zone  K  as  shown  in  Fig. 
Ill  with  a  magnification  of  117 
diameters. 

When  samples  are  taken  of  case- 
hardened  material,  it  is  much  more 
satisfactory  to  determine  the  depth 
of  the  case  by  microscopic  examination  and  then  plane  or  turn 
down  the  material  to  the  desired  depth,  analyzing  the  case  and 
the  core  separately,  than  it  is  to  attempt  to  get  a  representative 
sample  by  drilling  or  planing  the  whole  specimen. 

Decarbonizing. — Long  heating  in  an  oxygen-rich  atmosphere 
causes  a  change  which  is  exactly  the  reverse  of  that  just  described, 
and  is  of  almost  equal  importance  both  with  regard  to  getting 
representative  samples  of  the  material  for  analysis  and  in  deter- 
mining its  properties.  The  outer  surface  (and  sometimes  a 
layer  extending  some  distance  into  the  material)  becomes  decar- 
bonized and  changes  from  a  very  hard,  brittle  material  to  almost 
pure  iron,  which  is  characterized  by  its  softness.  The  decar- 


FIG.  110. — Section  of  case-hard- 
ened axle-bearing.     4  X- 


GENERAL  STUDY  OF  STEEL  WITH  THE  MICROSCOPE      397 

bonizing  effect  is  never  produced  intentionally,  but  often  occurs  in 
steel  which  has  been  annealed  either  for  too  long  a  time  or  at  too 
high  a  temperature.  Figure  112  shows  a  piece  of  cast  steel  in 
natural  size,  which  was  decarbonized  by  too  long  annealing. 


Carbon-rich 
outer  zone  R 


Carbon-poor 
inner  zone  K 


FIG.   111. — Transition  from  inner  to  outer  zone.      117  X. 

Etching  with  copper  ammonium  chloride  causes  a  darkening  of 
the  core  which  is  rich  in  carbon  and  thus  gives  a  good  idea  of  the 
depth  of  the  decarbonization.  The  transition  from  the  decar- 
bonized outer  layer  to  the  carbon-rich  inner  zone  is  shown  in  Fig. 


FIG.  112. — Steel  casting  superficially  decarbonized  by  too  long  annealing. 

113  with  a  magnification  of  117  diameters.  Microscopic  exami- 
nation gives  a  clear  idea  of  the  amount  of  decarbonization  with- 
out the  necessity  of  analysis.  Similar  phenomena  play  a  very 
undesirable  part  in  the  behavior  of  tool  steel.  The  decarboniza- 


398 


MICROSCOPIC  EXAMINATION  OF  METALS 


tion  is  often  confined  to  a  very  thin  layer  or  occurs  locally.  If 
this  partial  decarbonization  takes  place  exactly  where  hardness 
is  required,  difficulties  arise  which  can  be  overcome  only  if  the 


Decarbonized  outer 
zone  R 


Core  K,  rich  in 
carbon 


FIG.   113. — Transition  from  outer  to  inner  zone.     117  X- 

cause  is  known.  A  chemical  analysis  without  a  previous  metallo- 
graphic  examination  would  be  valueless  in  cases  of  this  sort,  where 
accidental  and  unexpected  local  changes  in  the  chemical  composi- 
tion of  the  steel  have  occurred. 


CHAPTER  XXVII 
IRON 

Reference  to  the  iron-carbon  diagram  (Fig.  59,  p.  356)  shows 
that  the  range  including  pig  and  cast  iron  extends  from  1.7  to  4 
or  5  per  cent  C.  The  cementite  which  separates  along  the  line 
CE  is  so  readily  decomposed  on  cooling  that  three  classes  of  iron 
are  recognized,  depending  on  the  cooling  rate  and  on  the  presence 
of  constituents  other  than  carbon.  These  classes  are  known 
from  their  general  appearance  as  white  iron,  gray  iron  and  mottled 
iron,  the  last  a  combination  of  the  other  two. 

White  iron  results  from  the  rapid  cooling  (quenching  or  chill 
casting)  of  the  metal,  and  has  the  white  fracture  and  the  hard, 
brittle  characteristics  of  cementite.  Its  formation  is  favored  by 
the  presence  of  manganese  and  sulfur  and  the  absence  of  silicon. 
White  iron  is  too  hard  and  brittle  for  common  use,  and  is  seldom 
found  in  small  castings.  It  is  often  produced  intentionally, 
however,  as  a  hard  facing  on  a  softer  core  as,  for  example,  in  the 
casting  of  car  wheels  or  the  surfacing  of  rolls.  In  cases  of  this 
sort  the  white  iron  is  associated  with  mottled  and  gray  iron  and 
the  microscope  is  of  great  value  in  determing  the  thickness  of  the 
chilled  (white  iron)  layer.  The  characteristics  of  chilled  castings 
are  illustrated  in  the  following  figures.  Figure  114  shows  the 
casting  in  natural  size,  and  illustrates  clearly  the  transition  from 
the  white  iron  of  the  chilled  surface  a,  through  the  mottled  iron 
section  0  and  into  the  final  gray  form  7.  The  three  zones  are 
shown  in  detail  in  Figs.  115,  116,  117,  Figure  115  is  a  section 
from  the  white  border,  magnified  350  diameters.  The  white 
areas  are  cementite,  and  the  dark  masses,  pearlite.  Figure  116 
shows  the  transition  zone  of  mottled  iron,  in  which,  in  addition  to 
the  cementite  and  pearlite,  small  patches  of  graphite  occur. 
Figure  117  corresponds  to  the  gray  part  of  the  casting,  and  shows 
large  masses  of  graphite  with  the  pearlite  and  almost  no  cementite. 

An  average  analysis  over  the  whole  cross-section  (a.  =  white 
edge,  |8  =  transition  zone  and  7  =  gray  iron  core)  would  be  of  no 
value  in  this  case.  It  is  sometimes  useful  to  know  the  composi- 
tion of  the  individual  layers  a,  /3  and  7,  and  to  get  this,  samples 

399 


400 


MICROSCOPIC  EXAMINATION  OF  METALS 


for  analysis  should  be  taken  from  each  of  the  zones.     After  the 
depth  of  the  layers  has  been  determined  by  the  microscope, 


FIG.   114.— Chilled  casting.     1   X- 

shavings  for  analysis  should  be  taken  from  the  gray  iron  first, 
either  by  planing  or  by  boring  and  in  the  same  way  from  mottled 


FIG.  115. — Section  made  from  white  border,  a,  in  Fig.  114.     350  X- 

iron.     The  thin  layer  of  white  iron  which  is  left  and  which  cannot 
be  machined  is  then  broken  to  pieces. 


IRON 


401 


In  addition  to  these  differences  in  physical  properties  and 
metallographic  structure  which  are  due  chiefly  to  variations  in  the 


FIG.  116. — Section  taken  at  the  transition  zone,  j8.     350  X. 

cooling  rate,  several  other  difficulties  sometimes  occur  in  the 
sampling  and  inspection  of  white  iron. 


FIG.   117. — Taken  at  the  part  7.     350  X. 

Formation  of  Globules  and  Nodules.— It  happens  not  infre- 
quently   that    in  pig    iron  and  in  large  castings,   well  formed 


402 


MICROSCOPIC  EXAMINATION  OF  METALS 


globules  or  nodules,  sometimes  as  large  as  a  walnut  and  quite 
different  from  the  rest  of  the  metal  in  composition,  separate  from 
the  matrix  and  remain  inclosed  in  the  pig  or  casting.  Sometimes 
they  are  in  close  contact  with  the  metal,  at  other  times  they  are 
contained  in  cavities  in  the  casting.  These  inclusions  are  always 
much  higher  in  phosphorus  than  the  matrix,  but  lower  in  silicon. 
Platz  studied  the  composition  of  globules  of  this  sort  and  found 
the  following  values: 


TABLE  XIII. — ANALYSES  OF  GLOBULES  AND  NODULES  ACCORDING  TO  PLATZ 


Gray  iron  with  white 
edge 

Mottled  iron 

Mottled  pig  iron 

Globules, 
per  cent 

Matrix, 
per  cent 

Globules, 
per  cent 

Nodules, 
per  cent 

Matrix, 
per  cent 

Globules, 
per  cent 

Matrix, 
per  cent 

Large 

Small 

Silicon  
Phosphorus.  . 
Manganese  .  . 

0.58 
1.82 
1.17 

0.54 
2.38 
1.22 

0.98 
0.29 

0.72 

0.58 
1.44 
1.02 

0.52 
0.66 
0.78 

0.86 
0.30 
0.70 

0.48 
1.65 
2.25 

0.85 
0.40 
1.92 

Because  of  their  high  phosphorus  content,  the  globules  have  a 
much  lower  melting  point  than  the  matrix.  When  the  matrix 
solidifies,  the  still-liquid  alloy  (phosphide  eutectic)  is  pressed 
into  the  contraction  cavities  where  it  hardens  in  the  shape  of 
spherical  masses. 

Crystal  Formation  in  Cavities. — The  pigs  of  low-spiegel, 
puddle  iron  with  5  to  7  per  cent  manganese  often  contain  internal 
cavities  filled  with  well-developed,  leaf-like  crystals.  When  the 
pig  is  first  broken  these  crystal  leaves  have  a  mirror  surface, 
which  on  contact  with  the  air  soon  becomes  coated  with  a  layer 
of  oxide,  brownish  yellow  to  deep  blue  in  color  and  so  thin  that 
it  can  be  neglected  as  far  as  its  effect  on  the  analytical  results  is 
concerned.  The  chemical  study  of  the  crystals  and  the  matrix 
always  shows  a  marked  difference  in  the  composition  of  the  two. 

Separations  on  the  Outer  Surface  of  White  Iron. — It  is  well 
known  that  when  molten  white  iron  is  allowed  to  stand,  small 
masses  of  metal,  which  are  very  different  from  the  matrix  in 
composition  separate.  Ledebur  found  lumps  weighing  more  than 
500  g.  in  white  pig  iron  rich  in  manganese  and  phosphorus. 


IRON 


403 


The  table  shows  that  these  lumps  are  largely  manganese  sulfide. 
They  solidify  while  the  matrix  is  still  liquid. 

TABLE  XIV. — ANALYSES  OF  THE  MASSES  SEPARATING  ON  THE  SURFACE  OF 

WHITE  IRON 


Manganese 

Sulfur 

The  lumps  contained  
The  matrix  contained  

up  to  9  per  cent 
3  to  4  per  cent 

up  to  3  per  cent 
0  .  3  per  cent  at  most 

Effect  of  Remelting  on  the  Chemical  Composition  of  White 
Iron. — It  would  not  be  correct  to  base  the  composition  of  the 
original  white  iron  on  the  composition  of  the  casting  made  from 
it  because  the  iron  changes  its  composition  very  materially 
when  it  is  remelted.  It  is  also  true  that  the  method  of  melting, 
whether  in  the  crucible,  open  hearth  or  cupola  furnace,  has  a 
marked  influence  on  the  final  composition. 

After  three  remeltings  of  white  iron  in  graphite  crucibles 
(3  parts  graphite  to  3.25  parts  clay)  the  following  changes  in 
composition  were  determined: 

TABLE  XV. — ANALYSES  BY  MULLER 


Carbon, 

Silicon, 

Manganese, 

per  cent 

per  cent 

per  cent 

Before  remelting.  .    . 

3  59 

0  07 

2  04 

After  first  remelting 

3  71 

0  57 

1  91 

After  second  remelting  

3.77 

0.76 

1.85 

After  third  remelting  

3.63 

1.07 

1.86 

The  original  white  iron  showed,  after  each  remelting,  a  strong 
separation  of  graphite  with  a  simultaneous  increase  in  silicon 
content  and  decrease  in  manganese  content.  After  four  re- 
meltings  the  white  iron  had  been  changed  completely  to  gray 
iron.  Unfortunately  the  corresponding  graphite  determinations 
were  not  carried  out. 

A  sample  of  Spiegel  with  about  12  per  cent  manganese  was 
melted  in  a  graphite  crucible,  and  allowed  to  cool  slowly  in  the 


404 


MICROSCOPIC  EXAMINATION  OF  METALS 


furnace.  After  breaking,  the  lower  half  showed  a  brilliant  white 
fracture  while  the  upper  half  gave  a  dull  gray  fracture.  Micro- 
scopic study  and  chemical  analysis  showed  that  in  the  upper 
half  a  marked  separation  of  graphite  had  occurred  while  the 
lower  half  had  remained  white.  The  total  carbon  content  of 
the  upper  half  was  increased  and  the  manganese  content  was 
reduced  throughout  by  about  2  per  cent.  (See  Table  XVI.) 

TABLE  XVI. — SPIEGELEISEN  WITH  12  PER  CENT  MANGANESE  AFTER  MELT- 
ING IN  A  GRAPHITE  CRUCIBLE 


Lower  half, 
per  cent 

Upper  half, 
per  cent 

Total  carbon 

5  43 

5  19 

Graphite  

0.31 

1.80 

Combined  carbon  

5.12 

3.39 

Manganese  

9  77 

9  61 

Silicon 

0  94 

0  88 

Figure  118  (magnified  350  diameters)  shows  the  structure  of 
the  lower  white  half  B.  Figure  119  (magnified  117  diameters)  is 
taken  from  the  upper  gray  half. 

Influence  of  Heat  on  the  Physical  Composition  of  White  Iron. — 
One  of  the  important  uses  of  white  iron  is  as  an  intermediate 
product  in  the  manufacture  of  malleable  iron  or  malleable 
castings.  If  white  pig  iron  is  held  for  a  long  time  at  700  to  800°C. 
(annealed),  a  decomposition  of  the  iron  carbide  (cementite)  and 
of  the  carbon  rich  solid  solution  (martensite)  takes  place.  Car- 
bon (temper  carbon)  and  iron  (ferrite)  separate.  The  carbon 
which  is  formed  under  these  conditions  is  chemically  identical 
with  graphite,  and  may  be  determined  in  the  same  way,  but  it 
gives  to  the  iron  physical  properties  which  are  markedly  different 
from  those  of  gray  iron  of  the  same  chemical  composition  in 
which  the  graphite  has  separated  in  flakes  instead  of  in  the  finally- 
divided  form  characteristic  of  temper  carbon.  Malleable  iron 
has  a  tensile  strength  nearly  twice  that  of  gray  iron  of  identical 
composition,  and,  instead  of  being  brittle  and  susceptible  to 
shock,  is  remarkably  resistant  to  shock  although  not  malleable 
in  the  sense  in  which  the  word  is  used  in  reference  to  steel. 
Decomposition  does  not  take  place  uniformly  throughout  the 


IRON 


405 


entire  mass  of  the  castings,  but  starts  at  individual  centers  and 
spreads  out  from  them.  In  this  process,  the  removal  of  the 
carbon  (black  heart)  is  not  intended,  but  merely  a  change  of 


FIG.  118.— White  spiegel.     350  X- 

the    combined    carbon   into   temper  carbon.     To    what    extent 
the  desired  result  is  obtained  can  be  shown  much  more  quickly 


FIG.   119.— Gray  spiegel.     117  X 

and  surely  by  metallography  than  by  chemical  analysis.  Figure 
120  shows  the  effect  of  heating  a  piece  of  white  pig  iron  for  108 
hr.  in  wood  charcoal.  Large  masses  of  temper  carbon  are 


406 


MICROSCOPIC  EXAMINATION  OF  METALS 


imbedded  in  the  ferrite,  and  in  addition  cementite  and  pearlite 
are  present. 


FIG.   120.— Annealed  malleable  cast  iron.     350  X. 


FIG.   121. — Malleable  casting. 

If  the  heating  takes  place  in  an  atmosphere  rich  in  oxygen 
(malleableizing),  a  simultaneous  decarbonization  takes  place  at 


IRON 


407 


the  surface  and  gradually  works  in  toward  the  center.  Figure  121 
shows  a  casting  treated  in  this  way.  It  shows  three  distinct 
layers  or  zones  with  varying  carbon  content:  (a)  a  zone  at  the 


FIG.  122.— 100  X. 


outside  edges  which  is  low  in  carbon  (Fig.  122) ;  (b)  a  transition 
zone  richer  in  carbon  (Fig.  122) ;  (c)  a  zone  at  the  center  where 
temper  carbon  has  deposited  (Fig.  123). 


FIG.   123. — Central  zone.      100  X- 


An  average  analysis  is  of  no  value  in  this  case  as  it  tells  noth- 
ing of  the  way  in  which  the  carbon  is  distributed.     It  is  best,  in 


408 


MICROSCOPIC  EXAMINATION  OF  METALS 


all  cases  where  an  annealed  piece  is  to  be  analyzed,  to  have  the 
chemical  analysis  preceded  by  a  metallographic  examination. 
The  chemical  analysis  of  the  malleable  casting  shown  in  Fig.  121 
gave  the  following  values : 

TABLE  XVII. — ANALYSIS  OF  A  MALLEABLE  CASTING 


Samples  for  analysis  taken 
from  the  core  c.     (See  Figs. 
121,  122  and  123.)   Per  cent 

Samples    for    analysis    taken 
from  the  outer  and  from  the 
transition   zones1   a   and   b. 
(See  Figs.  121,  122  and  123.) 
Per  cent 

Total  carbon  
Temper  carbon 

3.48 

2  60 

1.45 
0  96 

Combined  carbon  
Silicon                .  . 

0.88 
0  65 

0.49 
0  66 

Manganese  

0.04 

0  04 

Phosphorus  
Sulfur 

0.083 
0  22 

0.085 
0  224 

Copper.  . 

0.21 

0.22 

Nickel  .  . 

0.05 

0.05 

Many  analyses  indicating  the  separation  of  temper  carbon 
have  been  published.     In  addition  to  the  length  of  heating  and 

the  temperature,  the  chemical  com- 
position also  has  its  influence  on  the 
separation  of  temper  carbon. 

When  the  heating  is  done  with 
coke  or  coal,  the  sulfur  content 
usually  increases  because  of  the 
sulfur  in  the  heating  material. 
This  increase  takes  place  only  in  the 
outer  layer.  The  percentages  of 
manganese,  silicon  and  phosphorus 
M generally  stay  unchanged. 

I  *n  *^e  case  of  ^arge  Pieces>  tf  *^e 

heating  temperature  is  not  the  same 

in  all  places  or  if  the  piece  is  not  in 
good  contact  with  the  malleableiz- 
ing  agent  (e.g.,  ferric  oxide)  at  all  points,  it  may  happen  that 
some  places  are  only  partly  malleableized  or  not  malleableized 
at  all.  White,  hard  spots  are  left  in  the  casting  which  become 
unpleasantly  noticeable  when  the  piece  is  machined.  This  con- 


IRON 


409 


dition  is  sometimes  found  in  an  incompletely  annealed  wheel. 
In  one  spot  it  may  show  the  characteristics  of  white  iron  (see 
Fig.  115)  while  in  all  other  parts  of  the  casting  there  is  plenty 
of  temper  carbon.  (See  Fig.  71.) 

Tempering  is  often  produced  unintentionally.  Wiist1  describes 
an  interesting  case  of  this  accidental  annealing.  A  gas  retort  of 
white  iron  (Fig.  124)  was  exposed  for  a  long  time  to  the  action 
of  furnace  gases.  The  samples  taken  at  the  points  marked  1  to 
4  gave  the  following  values: 

TABLE  XVIII 


Samples 

taken  at 

1 
Per  cent 

2 
Per  cent 

3 

Per  cent 

4 
Per  cent 

Total  carbon       

3.39 

3.33 

3.04 

0.50 

Graphite  and  temper  carbon  
Combined  carbon  

0.48 
2.91 

1.05 

2.28 

2.10 
0.94 

0.47 
0.03 

Silicon 

0.73 

0  70 

0  66 

0  49 

Manganese  

0.48 

0.46 

0.44 

0.39 

Phosphorus  
Sulfur 

0.081 
0  128 

0.074 
0  159 

0.073 
0  23 

0.079 
0  498 

Oxygen  

0.05 

0.12 

0.35 

0.75 

The  shavings  taken  at  1  correspond  to  the  original  composi- 
tion of  the  iron.  A  decided  change  in  the  chemical  composi- 
tion has  been  produced  by  the  malleableizing  effect  of  the  flue 
gas.  The  greatest  change  has  taken  place  at  the  bottom  of  the 
retort  which  was  most  directly  exposed  to  the  action  of  the  hot 
gas.  The  total  carbon  grows  less  as  the  bottom  is  approached 
and  the  relative  amount  of  temper  carbon  increases.  The  silicon 
content  grows  steadily  smaller  and  there  is  an  increase  in  both 
the  sulfur  and  oxygen. 

The  effect  of  having  an  untrained  workman  take  samples  at 
random  from  the  retort  just  described  and  sending  them  to 
different  laboratories  for  a  report  on  the  composition  of  the 
retort  material  can  be  imagined.  The  result  would  be  a  series 
of  analyses  which  would  have  no  apparent  connection  with  one 
another.  Metallographic  examination  shows  at  once  the  reason 
for  the  varying  results. 

1  F.  WtiST,  Stahl  u.  Eisen,  1903,  1136. 


CHAPTER   XXVIII 
GRAY  IRON 

Influence  of  the  Cooling  Rate  on  the  Amount  and  Kind  of 
Graphite  in  Cast  Iron. — Ordinary  iron  castings  are  chiefly  gray 
iron,  which  has  been  so  named  because  of  the  gray  color  due  to 
the  separation  of  graphite  in  the  massive  form  (Figs.  117  and 
119),  but  as  in  the  case  of  white  iron  (p.  399)  the  amount  and 
kind  of  graphite  which  separates  in  gray  iron  depends  largely 
on  the  rate  of  cooling. 

Small  castings  will  show  a  lower  graphite  content  and  a  dif- 
ferent distribution  of  the  graphite  than  large  castings  made  from 
the  same  iron.  Even  at  the  same  cross-section,  when  the  total 
carbon  is  uniform  throughout,  the  graphite  content  on  the 
outer  edge  of  the  casting,  where  the  cooling  is  most  rapid,  is  often 
less  than  in  the  center. 

Since  the  amount  and  kind  of  graphite  determines  in  large 
measure  the  mechanical  properties  of  cast  iron,  it  is  often  nec- 
ossary  to  make  analyses  of  different  parts  (edge,  center,  etc.). 

Where  the  determination  of  graphite  is  the  principal  purpose 
of  the  analysis,  it  is  better  not  to  take  the 

. 

sample  by  planing  or  boring,  but  to  cut  out 
small  pieces  (sections  or  cubes)  as  shown  in  Fig. 
125.  In  this  way  the  sources  of  error  in  sam- 
pling and  weighing,  described  in  detail  on  p. 
436,  are  eliminated  without  complicating  the 
analytical  work  in  any  way. 

The  following  example1  shows  the  effect  of 
the  nature  of  the  cross-section  on  the  graphite  content.  It  hap- 
pens, also,  particularly  with  bars  of  greater  cross-section,  that 
there  is  less  separation  of  graphite  at  the  corners  because  of  the 
quicker  cooling  there. 

1  E.  HEYN,  Stahl  u.  Eisen,  1906,  1295. 

410 


Middle 


Edg< 


FIG.  125. 


GRAY  IRON 


411 


Bars  of  various  sizes  (%6  by  K 
in  one  piece  as  shown  in  Fig.  126. 
the  iron  used  was: 


Total  carbon. 

Silicon 

Manganese . . . 
Phosphorus.  . 
Sulfur.. 


to  6  in.  by  6  in.)  were  cast 
The  average  composition  of 


3 . 38  per  cent 
2.51  per  cent 
0.81  per  cent 
0 . 56  per  cent 
0 . 095  per  cent 


4 

<—  245—  -> 

m 

<r-195^» 

& 

05 

& 

:")" 

<a 
d 

B 

33 

55 

27    2 

! 
38 

!'ST« 

4a 

<rl55-> 

if 
1 

<—  1720  > 

FIG.   126.— Dimensions  in  millimeters.     Cf.  Table  XIX, 

For  the  determination  of  graphite,  samples  were  taken  from 
the  middle  and  from  the  edges  as  shown  in  Fig.  125.  These 
samples  were  in  the  form  of  small  pieces  weighing  about  2  g. 

2 


u 

?  '1 

Tot 

alC: 

rbon 

. 

] 

iidd 

e 

<f' 

^ 

V^ 

--' 

•°~~~ 



^v 

^ 

<%' 

^- 

*••>, 

Coi 

ner 

** 

-*~°^ 

0  9 

2 

) 

4 

9 

( 

0 

8 

0 

1 

30 

£ 

B 

1 

10 

16 

Cross-Section  Edge  in  mm 

FIG.  127. 

each.     The  results  are  given  in  the  following  table  and  shown 
graphically  in  Fig.    127. 


412 


MICROSCOPIC  EXAMINATION  OF  METALS 


Table  XIX  and  Fig.  127  show  that  the  graphite  content  is 
lowest  in  the  center  of  the  thinnest  bars.  It  increases  with 
increasing  cross-section  until  a  maximum  is  reached  at  2%  by 

TABLE  XIX. — ANALYSES  BY  E.  HEYN 


Center  of  bar 

Corner  of  bar 

Cross-section 

in  mm. 

Graphite 

Graphite 

Per  cent 

in  per  cent 

Per  cent 

in  per  cent 

Graphite1 

of  total  car 

Graphite 

of  total  car- 

bon 

bon 

155  X  155  (6        in. 

X  6         in.) 

3.00 

88.7 

2.68 

79.3 

130  X  130  (5H    in. 

X  5H    in.) 

3.00 

88.7 

2.68 

79.3 

105  X  105  (4>i    in. 

X  4^4    in.) 

2.97 

87.9 

2.92 

86.4 

85  X  85    (3%    in. 

X  3%    in.) 

3.06 

90.5 

2.95 

87.2 

65  X  65    (2%    in. 

X  2%    in.; 

3.03 

89.7 

2.85 

84.5 

55  X  55    (2${t  in. 

X  2^6  in.) 

2.98 

88.2 

2.94 

86.9 

44  X  44    (1%    in. 

X  1?4    in.) 

2.84 

84.0 

2.78 

82.2 

33  X  33    (IK  6  in. 

X  1%6  in.) 

2.77 

82.0 

2.62 

77.5 

27  X  27    (iKe  in. 

X  IK  6  in.) 

2.66 

78.7 

2.55 

75.5 

22  X  22    (  H    in. 

X     K    in.) 

2.55 

75.5 

2.55 

75.5 

16  X  16    (  H    in. 

X      %  in.) 

2.55 

75.5 

2.53 

74.8 

12  X  12    (  Ke  in. 

X     He  in.) 

2.50 

74.0 

Sample    from    the    whole 

cross-section 

1  The  value  given  is  in  each  case  an  average  of  from  two  to  five  separate  determinations. 
Each  determination  was  made  on  a  new  section. 


in.     Investigation  seems  to  indicate  that  under  the  conditions 
of  the  experiment  (casting  temperature,  cooling  rate,  and  silicon, 


50 

a  45 

i« 

5  35 

I" 

"25 

2. 

IS 

I 

1 

\ 

\ 

0? 

N 

^ 

-<i—-_ 

•5  —  . 

0 

"~~"° 

20      40       60       80       100     12D     140     160 
Cross  Section  Edge  iu  mm 

FIG.  128. 


content  of  the  iron)  the  cross-section  2%  by  25^  in.  is  large 
enough  to  allow  the  maximum  graphite  separation  in  the  core 


GRAY  IRON  413 

of  the  bar.  At  the  corners  of  the  larger  bars,  where  the  rate  of 
cooling  is  considerably  greater  than  in  the  center,  the  graphite 
content  is  much  lower  than  in  the  center.  With  the  small 
bars  where  the  rate  of  cooling  is  approximately  the  same  through- 
out, the  differences  in  graphite  content  in  different  parts  of  the 
bar  disappear. 

That  accidents  also  have  considerable  influence  on  the  graphite 
separation  at  the  corners  of  the  bars  is  shown  by  the  fairly  wide 
variations  in  the  analytical  results. 

Not  only  the  amount  of  graphite  present  but  also  the  shape  and 
size  of  the  individual  graphite  plates  may  influence  the  physical 
properties  of  cast  iron.  Chemical  analysis  gives  no  indication  of 
the  size  or  shape  of  the  graphite  plates  so  that  here  again  metal- 
lography must  come  to  the  aid  of  the  chemist  in  explaining  un- 
usual conditions  such  as  the  differences  in  tensile  strength  of 
pieces  of  iron  of  identical  chemical  composition.  The  trans- 
verse strength  of  the  bar  shown  in  Fig.  126  is  given  in  Fig.  128. 

The  transverse  strength  is  greatest  in  the  bar  with  the  smallest 
cross-section.  This  decreases  with  increasing  graphite  content. 
In  castings  larger  than  2%  by  2%  in.  (the  size  at  which  the 
graphite  content  reaches  its  maximum  and  beyond  which  there 
is  no  change)  there  is  a  clearly  marked  decrease  in  the  trans- 
verse strength  with  increasing  size.  Metallographic  study 
explains  these  facts,  as  is  shown  in  Fig.  129.  The  linear  magnifi- 
cation is  the  same  in  all  cases  (117  diameters). 

The  photographs  show  very  clearly  that  with  increasing  cross- 
section  the  size  of  the  individual  graphite  crystals  increases. 
The  difference  between  the  bar  with  the  largest  cross-section 
and  the  bar  with  the  smallest  cross-section  is  very  marked.  It 
is  obvious  that  graphite  plates  of  the  length  and  size  found  in 
the  bar  with  the  largest  cross-section  would  break  up  the  contin- 
uity of  the  iron  and  so  tend  to  weaken  the  tensile  strength. 

If  the  number  of  graphite  plates  occurring  in  0.0016  sq.  in.  of 
surface  in  each  bar  is  determined  and  these  numbers  are  plotted 
as  ordinates  and  the  thicknesses  of  the  bars  are  used  as  abscissas, 
the  graphical  results  of  the  experiments  described  above  are 
shown  in  Fig.  130.  The  number  of  graphite  grains  is  greatest  in 
the  bars  with  the  smallest  cross-section  and  least  in  the  largest 
ones.  The  number  of  graphite  grains  is  greatest  at  the  edges 


414  MICROSCOPIC  EXAMINATION  OF  METALS 


Rod 


Rod  6"X6' 


FIG.  129. — Influence  of  thickness 


GRA  Y  IRON 


415 


Rod  6"X  6* 


on  the  separation  of  graphite. 


416 


MICROSCOPIC  EXAMINATION  OF  METALS 


and  corners  in  spite  of  the  fact  that  the  total  graphite  content 
is  smallest  at  these  points.  The  individual  graphite  crys- 
tals must  be  smaller  in  size  in  the  small  rods  and  at  the 
corners  of  the  larger  ones  than  at  the  center  of  the  larger  bars. 
The  results  obtained  by  counting  the  individual  graphite  plates 
is  in  complete  agreement  with  the  results  obtained  by  the 
metallographic  study. 

The  following  example  illustrates  very  clearly  the  influence  of 
the  size  of  the  bar  on  the  graphite  content.  It  is  taken  from 
an  investigation  by  Jiingst.1  Seven  round  bars  from  %Q  to  2 


400 


300 


100 


40  60  80  100  120 

Thickness  of  Bar  in  mm. 

FIG.  130. 


140 


160 


in.  in  diameter,  cast  at  the  same  time  from  a  mixture  with 
1.93  per  cent  silicon,  0.55  per  cent  manganese,  0.712  per  cent 
phosphorus,  and  0.090  per  cent  sulfur  gave  the  following  values: 


ANALYSES  BY  JUNGST 


2  in. 

IHin. 

l^in. 

%  in. 

Me  in. 

Hi*. 

Me  in. 

Per  cent 

Per  cent 

Per  cent 

Per  cent 

Per  cent 

Per  cent 

Per  cent 

Graphite 

2  95 

2  90 

2  82 

2  80 

2  60 

2  60 

2  39 

Combined  carbon  .... 
Total  carbon  

0.42 
3  37 

0.50 
3  40 

0.60 
3  42 

0.60 
3  40 

0.72 
3  32 

0.78 
3.38 

0.99 
3.38 

The    graphite    content    decreases    regularly   with   increasing 
cross-section,  the  percentage  of  combined  carbon  increases  and 
1  JUNGST,  Stahl  u.  Eisen,  1906,  p.  415. 


GRAY  IRON 


417 


the  percentage  of  total  carbon  stays  about  the  same.  (See  also 
Fig.  131.)  Jiingst's  results  do  not  show  any  marked  differences 
in  graphite  content  between  the  edges  and  the  middle  of  the 
specimen.  The  arrangement,  number  and  size  of  the  graphite 
plates  are  markedly  different  at  the  edges  and  at  the  core  of  the 
specimens. 

The  following  example1  is  also  interesting  as  it  shows  clearly 
that,  especially  with  gray  iron,  the  chemical  analysis  alone  often 
fails  to  explain  unusual  behavior. 


To 


tal  Carboi 


G**t 


10        15        20       25        30       35       40 
Diameter  of  the  Bar  in  mm. 

FIG.  131. 


45      50 


Cast  iron  rich  in  silicon  was  cast  in  a  sand  mold  fitted  with  an 
iron  bottom  so  that  quenching  experiments  could  be  made.  The 
mold  was  open  at  the  top. 

The  fracture  of  the  piece  showed  in  the  upper  part  (see  Fig.  132) 
a  very  coarse  grain  with  large  graphite  plates;  the  lower  part  of 
the  specimen  showed  a  sudden  transition  from  the  coarse  to  a 
fine  structure  in  which  the  graphite  plates  were  not  visible. 
Chemical  analysis  of  the  upper  and  lower  parts  showed  the 
composition  of  the  two  parts  to  be  practically  identical  in  spite 
of  the  marked  difference  in  the  appearance  of  the  fracture. 
As  a  result  of  microscopic  examination  of  the  two  parts,  it  was 
found  that  the  coarse-grained,  upper  part  was  filled  with  long, 
large  graphite  leaves  (Fig.  133)  while  the  lower  part  showed  the 

1  E.  HEYN,  Stahl  u.  Eisen,  1906,  p.  1295. 
27 


418 


MICROSCOPIC  EXAMINATION  OF  METALS 


eutectic  appearance  and  probably  corresponded  to  a  true  graphite 
eutectic  (Fig.  134).  The  mechanical  properties  of  the  two  parts 
were  very  different. 

Influence  of  Remelting  on  the  Chemical  Composition  of  Gray 
Iron. — The  chemical  composition  of   gray  iron  is  changed  by 

remelting,  although,  be- 
cause of  the  greater 
stability  of  graphite  as 
compared  with  cementite 
the  changes  in  the  physical 
properties  are  not  nearly  so 
marked  as  with  white  iron 
(p.  403).  If  a  cupola  fur- 
nace is  used,  in  remelting 
the  manganese  is  most 
readily  oxidized,  while  the 
silicon,  if  the  manganese 
is  still  high,  will  be  affected 
but  slightly.  With  high 
manganese  content  an  in- 
crease in  silicon  may  occur 
due  to  reduction  of  the  slag. 
The  silicon  does  not  be- 
gin to  burn  until  most  of 
the  manganese  has  been 
oxidized. 

Carbon  will  stand  a 
longer  heating  in  the  cupola 
furnace  where  the  iron  is  in 
immediate  contact  with  the 
hot  coke,  from  which  carbon 
can  be  taken  as  fast  as  it  is 
used  up,  than  in  the  rever- 
beratory  furnace  where  ox- 
idation takes  place  quickly.  With  high  manganese,  the  carbon 
content  is  likely  to  increase.  Sulfur  generally  increases  due  to 
the  presence  of  sulfur  in  the  products  of  combustion,  while  the 
phosphorus  content  usually  changes  but  little.  Because  of  these 
various  changes,  the  analysis  of  the  original  material  from  which 


FIG.   132. — Fractured  casting. 


GRAY  IRON 


419 


a  casting  is  made  may  give  only  an  approximate  idea  of  the 
composition  of  the  finished  casting. 


FIG.  133.— Upper  half.     350  X- 


Influence  of  Annealing  on  Gray  Iron. — Long-continued  heat- 
ing,  at   annealing   temperatures    (above    1,000°C.)    and   in   an 


FIG.  134. — Lower  half.     350  X. 


atmosphere  rich  in  oxygen,  can  cause  marked  changes  in  the 
composition  of  gray  iron,  especially  in  the  carbon  content.     An 


420  MICROSCOPIC  EXAMINATION  OF  METALS 

iron  casting  containing  3.66  per  cent  carbon,  of  which  2.02  per 
cent  was  in  the  form  of  graphite,  was  annealed  seven  times  at 
temperatures  of  about  1,000°,  and  at  the  end  showed  a  drop  in 
total  carbon  to  0.10  per  cent  and  of  graphite  to  0.02  per  cent. 
At  the  same  time  the  sulfur  had  increased  from  0.157  to  0.781 
per  cent  In  addition  to  the  burning  of  the  carbon  under  these 
conditions,  it  has  been  suggested  that  there  is  a  slagging  and 
segregation  of  the  phosphorus.  This  is  not  at  all  impossible  as 
the  ternary  eutectic  (solid  solution-carbide-phosphide)  begins 
to  melt  at  950°. 

Abnormal  Formations  in  Gray  Iron. — Growths  of  various 
sorts  occur  with  gray  iron  much  as  they  do  with  white  iron,  and 
their  effects  on  the  properties  and  methods  of  sampling  are 
essentially  the  same.  Globules  or  nodules  varying  in  size  from 
that  of  flax  seed  to  masses  one-fourth  of  an  inch  in  diameter, 
may  be  formed  on  the  surface  of  the  iron.  These  masses  differ 
widely  from  the  main  casting  in  composition  and  are  always 
high  in  phosphorus.  Well-defined  crystals  are  sometimes  found 
in  cavities  in  the  iron,  and  do  not  differ  materially  from  the 
composition  of  the  casting  except  that  they  are  apt  to  be  covered 
with  a  white  coating,  which  is  nearly  pure  silica  and  which 
would  seriously  influence  the  analysis  of  the  sample  if  the  crystal 
should  happen  to  be  included  in  the  part  selected.  In  depres- 
sions on  the  sides  of  the  pig  where  the  iron  is  in  contact  with  the 
sand  mold,  mossy  or  asbestos-like  growths  of  a  yellowish  white 
color  are  sometimes  formed.  These  masses  are  found  to  be 
largely  silica,  though  they  often  contain  titanium  and  potassium. 
It  has  been  suggested,  as  a  possible  reason  for  these  masses, 
that  a  volatile  silicon  compound,  probably  silicon  sulfide,  is 
formed  in  pig  iron  and  that  when  this  compound  comes  in 
contact  with  the  air,  the  sulfur  burns  to  sulfur  dioxide  and  the 
silicon  forms  silica  which  deposits  on  the  colder  walls  of  the  pig 
or  in  the  cavities. 

These  various  irregularities  in  gray  iron,  both  the  normal 
changes  due  to  remelting  or  annealing  and  the  abnormal  for- 
mations just  described,  indicate  again  the  importance  of  pre- 
ceding the  chemical  analysis  by  a  metallographic  examination, 
if  possible,  in  order  to  be  certain  that  the  sample  is  homogeneous 
or,  if  it  is  not,  to  determine  the  nature  and  distribution  of  abnor- 


GRAY  IRON 


421 


mal  deposits  so  that  the  chemist  may  know  what  his  analysis 
really  represents. 

Disintegration  of  Cast  Iron. — A  more  unusual  cause  of  unsatis- 
factory results,  the  disregard  of  which  may  cause  serious  analy- 
tical errors,  is  the  phenomenon  of  disintegration  which  often 
occurs  under  service  conditions. 

If,  for  example,  a  cast-iron  water  main  lies  for  a  number  of 
years  in  contact  with  moist  earth,  a  curious  decomposition  takes 
place.  In  certain  spots  on  its  surface  the  pipe,  without  losing 
its  form,  will  change  to  a  dull-gray  mass  so  soft  that  it  can  be 
cut  with  a  knife.  The  reason  for  this  change  has  not  been 
satisfactorily  explained.  Moisture  is  absolutely  necessary, 
but  whether  the  change  is  due  chiefly  to  oxidation  or  to  stray 
electric  currents  is  still  an  open  question.  The  following  table 
shows  the  marked  difference  in  composition  between  the  corroded 
and  uncorroded  parts  of  the  pipe. 

TABLE  XX 


In  original 

At  the  cor- 

casting, 

roded  spots, 

per  cent 

per  cent 

Total  carbon  

2.50 

8.10 

Silicon  

2  66 

9  30 

Phosphorus  

1.90 

6.50 

Iron  

46.18 

A  similar  effect  is  sometimes  noticed  with  castings  which  have 
been  exposed  to  heat.  The  cast-iron  coils  of  a  hot-water  heater 
which  had  been  exposed  to  the  hot  gases  of  the  flame  showed 
spots  soft  enough  to  be  scraped  off  with  a  knife,  especially  at  the 
threaded  joints.  Analysis  of  the  soft  material  indicated  clearly 
that  it  was  a  decomposition  product  of  pig  iron,  the  total  carbon 
amounting  to  about  12  per  cent,  while  the  iron  had  dropped  to 
about  39  per  cent  almost  wholly  combined  with  oxygen. 

Figure  135  shows  a  badly  corroded  gray  cast  iron  magnified  to 
350  diameters.  The  original  graphite  leaves  appear  light  gray 
in  contrast  to  the  dark  background. 


422 


MICROSCOPIC  EXAMINATION  OF  METALS 


Mottled  Iron. — Since  mottled  iron  is  an  intermediate  product 
between  white  and  gray  irons,  its  sampling  and  analysis  will  be 
subject  to  the  difficulties  of  both.  It  is  especially  likely  to  have 


FIG.   135. — Decomposed  cast  iron.     350  X. 

the  graphite  and  cementite  masses,  of  which  it  is  composed,  irregu- 
larly distributed  through  the  casting,  so  that  the  selection  of  a 
representative  sample  is  one  of  much  difficulty. 


CHAPTER  XXIX 


SAMPLING  OF  IRON  AND  STEEL 

Many  of  the  difficulties  connected  with  the  selection  of  really 
representative  samples  of  steel  and  iron  have  been  mentioned 
in  connection  with  the  macroscopic  and  microscopic  study  of  the 
metals,  and  suggestions  have  been  made  as  to  the  best  means  of 
taking  the  samples  in  special  cases.  It  may  be  of  service  to  the 
analyst,  however,  to  have  this  information  assembled  and  to 
consider  in  a  general  way  the  methods  used  in  the  plant. 

General  Discussion  of  Sampling. — As  a  general  rule  for  all 
metals  that  can  be  worked  with  a  cutting  tool,  a  better  representa- 
tive sample  can  be  obtained  by 
plaining  over  the  whole  cross- 
section  than  by  drilling,  turn- 
ing, etc.,  and  when  a  metallo- 
graphic  study  has  preceded 
the  chemical  analysis,  the 
shavings  should  be  taken  from 
the  place  adjoining  that  from 
which  the  specimen  was  taken 
for  microscopical  study.  Figure  136  shows  the  method  used  in 
taking  a  sample  from  a  steel  rail. 

If  marked  irregularities  are  found  by  the  microscopic  study, 
it  may  be  desirable  under  certain  conditions  to  get  samples  from 
different  parts  of  the  specimen,  in  which  case  drilling,  turning, 
etc.,  may  be  necessary.  If  merely  an  average  analysis  is  required, 
however,  planing  of  the  whole  surface  is  enough.  In  reporting 
a  complete  analysis,  an  exact  statement  should  be  given  of  the 
method  of  sampling,  with  an  explanatory  sketch  if  necessary. 
A  sketch  is  indispensable  if  shavings  have  been  taken  from 
different  parts  of  the  specimen  (core,  outer  zone,  etc.). 

Frequently,  far  too  little  care  is  taken  with  the  purely  mechan- 
ical part  of  taking  samples,  cleaning  of  the  test  specimen,  plan- 

423 


FIG.  136. — A.  Section  for  metallo- 
graphic  study.  The  surface  indicated 
by  the  cross-hatched  line  is  ground, 
polished  and  etched.  B.  Shavings  for 
analysis  are  obtained  by  planing  the 
whole  cross-section. 


424  MICROSCOPIC  EXAMINATION  OF  METALS 

ing  and  collecting  samples,  in  spite  of  the  fact  that  many  serious 
errors  can  be  introduced  by  careless  work.  The  first  requisite 
is  naturally  that  the  planer  should  be  clean,  that  no  shavings 
from  previous  tests  are  on  it,  and  that  all  parts  that  come  in  con- 
tact with  the  specimen  are  free  from  oily,  fatty,  or  soapy  matter. 
Care  must  also  be  used  to  see  that  no  oil  or  grease  drops  on  the 
shavings  already  made. 

Cleaning  the  Surface  of  the  Test  Piece. — Before  taking  a 
sample  the  surface  of  the  piece  must  be  examined  carefully  for 
external  impurities  and  freed  from  any  that  may  be  found. 
First  come  the  substances  that  adhere  loosely,  e.g.,  sawdust 
from  the  packing,  dirt,  in  case  the  specimen  has  lain  on  the 
ground,  and  similar  impurities.  These  can  often  be  removed  by 
washing  or  by  rubbing  with  a  stiff  brush  or  polishing  cloth. 
Paint  or  shellac,  letters,  numbers,  as  well  as  rust  spots,  can  be 
removed  by  means  of  a  wire  brush  or,  if  necessary,  by  using  a 
solvent  for  the  paint  (alcohol,  ether,  gasolene,  kerosene),  but 
only  those  solvents  should  be  used  which  do  not  attack  iron. 

Surface  coatings  produced  during  the  manufacture,  e.g.,  casting 
skin,  forge  scale,  etc.,  adhere  much  more  firmly  than  accidental 
impurities.  If  they  cannot  be  removed  by  the  steel  wire  brush, 
it  is  necessary  to  hammer,  file,  or  rub  with  emery  cloth.  In 
such  cases  care  should  be  taken  not  to  remove  large  quantities 
of  material. 

Planing  and  Collecting  the  Shavings. — If  the  material  is 
hard,  the  speed  of  the  planer  should  not  be  too  fast  or  the  tension 
too  high,  as  otherwise  the  shavings  are  apt  to  fly  off  and  be  lost, 
and  there  is  the  additional  danger  that  pieces  of  the  cutting  tool 
may  break  off  and  contaminate  the  sample.  If  a  piece  of  the 
cutting  tool  should  fall  into  the  sample  and  be  weighed  with  it, 
incorrect  results  would  be  obtained  without  any  reason  apparent 
to  the  analyst.  It  is  scarcely  necessary  to  say  that  shavings 
which  have  fallen  on  the  floor  should  not  be  used  for  analysis, 
as  the  chance  of  contaimination  is  too  great.  The  greatest  care 
should  be  used  in  the  taking  and  collecting  of  samples  in  the  shop. 

In  planing  certain  kinds  of  iron,  the  untrained  workman  is 
likely  to  pick  up  only  the  coarser  shavings,  leaving  the  finely 
powdered  material,  e.g.,  graphite  in  cast  iron  or  slag  in  wrought 
iron,  on  the  bench  or  even  blowing  it  away.  The  fact  that  very 


SAMPLING  OF  IRON  AND  STEEL  425 

serious  errors  can  be  introduced  in  this  way  will  be  shown  on  pp. 
432  and  433. 

To  avoid  losses,  it  is  a  good  plan  to  place  strong,  glazed  paper 
around  the  test  piece,  as  shown  in  Fig  137.  Then,  if  the  cutting 
speed  and  tension  are  properly  chosen  so  that  the  shavings  do 
not  spring  away  during  the  planing,  the  coarse  shavings  as  well 
as  the  powdery  material  will  fall  into  the  paper  and,  after  the 
removal  of  the  test  piece,  may  be  shaken 
into  a  bottle  without  danger  of  loss. 

Annealing  before  Taking  the  Sample. — 
Hardened  steel  is  often  annealed  before  planing, 
to  make  it  more  easily  machined.  The  anneal- 
ing temperature  in  the  case  of  carbon  steel  is 
such  that  it  will  be  above  the  pearlite  point 
(700°C  with  pure  carbon  steel) .  A  quarter  of 
an  hour's  annealing  at  750  to  800°C  followed 
by  a  slow  cooling  until  the  pearlite  point  is 
reached  is  enough.  Below  600°C  the  cooling  can  take  place 
quickly,  for  with  carbon  steels  even  quenching  in  water  will  not 
noticeably  increase  the  hardness  in  this  temperature  range. 

The  following  table  may  serve  as  an  aid  in  determining  the 
approximate  temperature.1 

Dull  red  heat about    525°  to  550°C 

Dark  red  heat about    700° 

Dull  cherry  red about    800° 

Cherry  red about    900° 

Bright  cherry  red , .  about  1000° 

Dark  orange about  1100° 

Bright  orange about  1200° 

White  heat about  1300° 

Bright  white  heat about  1400° 

Dazzling  white  heat about  1600° 

The  heating  can  take  place  in  an  open  charcoal  fire.  If 
it  is  done  in  a  furnace  (tube  furnace,  muffle  furnace,  etc.),  it 
is  advisable,  in  order  to  avoid  the  formation  of  forge  scale  with 
a  consequent  superficial  decarbonization,  to  place  pieces  of 

1  Exact  temperature  measurements  are  made  with  a  thermoelement.  For 
details  concerning  these  measurements,  consult  "The  Measurement  of 
High  Temperatures"  by  G.  K.  Burgess  and  H.  Le  Chatelier. 


426  MICROSCOPIC  EXAMINATION  OF  METALS 

charcoal  before  and  behind  the  test  piece.  The  air  entering  the 
furnace  must  then  pass  over  hot  carbon  so  that  the  oxygen  is 
burned  to  carbon  monoxide.  The  formation  of  forge  scale  can 
be  prevented  almost  entirely  in  this  simple  way.  The  fear  that 
superficial  carbonization  (cementation)  of  the  test  piece  can 
be  produced  in  this  way  by  the  carbon  monoxide  is  unfounded. 
A  very  much  longer  time  would  be  required  to  produce  an  ap- 
preciable cementation  effect.1 

It  should  be  stated  that  the  presence  of  certain  elements  in 
the  steel,  e.g.,  manganese  and  nickel,  causes  a  material  lowering 
of  the  pearlite  point.  In  such  cases  care  must  be  taken  in  the 
cooling  after  annealing. 

The  Sampling  of  Materials  which  Cannot  Be  Machined. — 
Certain  alloys  and  self-hardened  steel  cannot  be  machined  with 
ordinary  steel  tools,  even  after  annealing  and  slow  cooling. 
White  cast  iron  cannot  be  annealed  because  of  the  possible  separa- 
tion of  temper  carbon.  In  some  cases  special  tool 
steel  can  be  used  (chrome-tungsten  and  similar 
alloy-steels).  The  usual  precautions  should  be 
taken. 

If,  however,  the  material  cannot  be  worked 
either  with  carbon  steel  or  any  of  the  special 
steels,  it  is  necessary  to  knock  off  small  pieces 
from  different  parts  of  the  sample  and  to  pul- 
verize these  pieces.  This  pulverizing  can  usually 
be  done  with  a  heavy  hammer  on  a  steel  anvil. 
If  the  specimen  is  very  large  and  heavy,  a  trip 
hammer  is  sometimes  needed.  To  avoid  scatter- 
FIG.  138.  mS  the  small  fragments,  the  sample  should  be 
wrapped  in  heavy  linen  cloth.  If  a  trip  hammer 
is  used,  a  piece  of  iron  should  always  be  put  between  the  test 
specimen  and  the  hammer,  to  avoid  possible  injury  to  the 
machine.  The  broken  pieces  must  be  carefully  cleaned  to  free 
them  from  linen  fibers.  The  final  powdering  of  the  sample  can 
be  accomplished  in  a  diamond  mortar,  the  simplest  form  of  which 
is  shown  in  Fig.  138.  The  powder  obtained  after  treatment  of 

1  cf.  BAUER,  cf  Stahl  u.  Eisen,  1909,  No.  18  has  never  succeeded  in 
detecting  by  metallographic  means  the  slightest  trace  of  superficial  carbon- 
ization after  15  min.  annealing  in  contact  with  charcoal. 


SAMPLING  OF  IRON  AND  STEEL 


427 


the  larger  lumps  is  coned  up  and  quartered  as  in  the  usual  way 
of  sampling  powdered  ores. 

Sampling  of  Material  in  Wire  Form. — If  the  material  is  in 
the  form  of  thick  wire,  it  is  beaten  out  on  the  anvil  until  it  is  in 
the  form  of  thin  sheets  which  can  be  cut  with  tin-smith's  shears. 
Each  wire  is  then  cut  into  pieces  of  approximately  the  same 
length.  For  the  final  sample  one  or  two  of  these  shorter  pieces 
from  each  coil  are  taken  and,  after  thorough  mixing,  are  cut  into 
still  smaller  pieces  for  the  final  weighing.  If  there  is  doubt,  or 
if  the  metallographic  examination  shows  that  the  wires  are  not  all 
alike,  it  is  useless  to  take  an  average  sample.  In  this  case  a 
number  of  small  sections  should  be  cut  from  the  long  wire  and 
treated  separately. 

Sampling  from  the  Molten  Metal. — If  it  is  a  question  of 
getting  a  representative  sample  from  a  large  heat,  it  is  safest 
to  prepare  two  test  ingots  of  12  to  18  Ib.  in  weight,  one  at  the 
beginning  and  one  at  the  end  of  the  pour.  With 
a  very  large  heat,  a  third  sample  taken  at  the 
middle  of  the  pour  is  advisable.  The  small  -ingots 
are  cut  through  the  center  lengthwise  as  shown  in 
Fig.  139.  Samples  are  obtained  by  planing  over 
the  surface  indicated  by  the  shaded  line  in  the 
figure.  The  shavings  from  the  different  ingots 
are  united  to  make  a  single  average  sample. 
Under  certain  conditions  it  is  better  to  analyze 
each  ingot  separately  and  take  a  mean  of  the 
results.  It  is  possible  to  determine  in  this  way 
whether  or  not  segregation  took  place  when  the 
charge  was  in  the  molten  condition,  a  thing 
which  ought  not  to  occur  if  the  temperature  is 
high  enough. 

Instead  of  following  the  method  just  described, 
the  United  States  Steel  Corporation1  takes  a  ladle  test  during  each 
heat  when  approximately  one-half  of  the  metal  has  been  poured. 
One  of  two  types  of  sample  mold  is  used  to  receive  the  melted 
metal.  The  first  is  a  split  mold,  into  which  an  ingot  of  about  1^ 
sq.  in.  cross  section  and  534  m-  long  is  poured.  The  mold  is  pro- 

1  U.  S.  Steel  Corp.,  "Methods  for  the  Commercial  Sampling  and  Analysis 
of  Plain  Carbon  Steels." 


FIG.  139. 


428  MICROSCOPIC  EXAMINATION  OF  METALS 

vided  with  a  flare,  extending  about  3  in.  above  the  test  bar,  to 
serve  as  a  shrink  head  for  the  molten  metal.  The  second  type 
is  a  cast-iron  or  steel  ladle,  3%  in.  inside  diameter  at  the  top, 
2J£  in.  at  the  bottom  and  Y±  in.  deep.  In  both  cases  drillings 
are  taken  with  a  %-in.  drill.  The  test  bar  from  the  mold  of 
the  first  type  is  drilled  at  a  point  from  1  to  2J^  in.  from  the 
bottom  of  the  bar.  The  sample  ingot  of  the  second  type  is 
drilled  from  the  bottom  and  to  a  depth  not  greater  than  1  in. 
In  both  cases  special  care  is  taken  to  prevent  scale  from  getting 
into  the  sample. 

Sampling  of  Forged  or  Rolled  Material. — If  the  shape 
of  the  piece  to  be  analyzed  allows,  the  sample  for  average  com- 
position should  be  taken  by  planing  over  the  entire  cross-section, 
not  by  boring  or  drilling.  If,  on  the  other  hand,  an  average 
analysis  is  not  needed,  but  the  inspector  wishes  to  know 
whether  and  to  what  extent  segregation  has  taken  place,  or 
whether  there  are  other  irregularities  in  the  chemical  composi- 
tion of  the  material,  a  metallographic  examination  should 
precede  the  sampling. 

It  would  be  wholly  misleading,  for  instance,  to  take  samples 
from  a  rolled  rod  by  turning  off  the  outer  layer  as  indicated  in 

Fig.  140.  If  zone  formation 
has  taken  place,  due  to  segre- 
gation, an  analysis  of  turn- 
ings taken  at  the  point  d  on 
the  outer  zone  R  would  give 
FIG.  140.  an  entirely  false  idea  of  the 

average    composition  of    the 

bar,  as  that  point  represents  the  part  of  the  bar  in  which  segre- 
gation is  least  strongly  marked.  If  now,  in  order  to  make  a 
control  analysis,  the  rod  was  turned  down  still  more  (e  in  Fig. 
140)  the  analyst  would  find  much  higher  percentages  of  phos- 
phorus and  sulfur,  assuming  that  segregation  had  taken  place 
as  indicated. 

Rolled  material  is  especially  liable  to  contain  segregated 
areas,  as  in  the  case  of  the  round  rod  just  referred  to,  but  the 
nature  and  distribution  of  this  segregated  material  varies  so 
widely  in  different  pieces  that  only  one  or  two  examples  can  be 
given  to  indicate  the  general  nature  of  the  difficulty  and  to 


SAMPLING  OF  IRON  AND  STEEL 


429 


ICO 


I 


H 


col 


430 


MICROSCOPIC  EXAMINATION  OF  METALS 


emphasize  again  the  necessity  of  extreme  care  and  judgment  in 
the  selection  of  the  sample  for  analysis. 

It  frequently  happens  that  the  segregated  areas  are  not 
sharply  marked,  but  that  smaller  or  larger  segregated  spots  are 
irregularly  distributed  throughout  the  whole  cross-section  area. 
In  this  case  there  is  no  distinct  division  into  an  inner  and  outer 
zone.  Figure  141  shows  the  sulfur  prints  on  silk  of  three  plates, 
in  which  the  segregation  stripes  are  irregularly  distributed. 
Analysis  gave: 

TABLE  XXI 


Sample  taken 

Phosphorus, 
per  cent 

Sulfur, 
per  cent 

Over  the  whole  cross-section  

0.078 

0.060 

From  the  segregated  streaks  

0.183 

0.101 

In  all  these  cases,  representative  samples  could  be  taken  by 
planing  over  the  whole  cross-section.  In  some  cases,  however, 
even  shavings  made  by  planing  over  the  whole  cross-section 
do  not  represent  the  average  composition  of  the  material. 


FIG.  142. 


FIG.   143. 


If  a  slab  with  an  inner  zone,  K,  like  that  indicated  in  Fig.  142, 
is  rolled  out  to  a  plate,  the  inner  zone  tapers  toward  the  ends  and 
sides  of  the  plate,  as  indicated  in  the  sketch,  Fig.  143,  and  in  the 
photograph,  Fig.  144. 

If  now,  for  the  purpose  of  getting  samples,  the  entire  section 
is  planed  over  at  the  place  "a"  in  Fig.  143  the  analysis  will  not 
show  the  true  average  composition  of  the  material  in  spite  of  the 
apparently  correct  sampling,  because  the  shavings  really 
represent  only  the  outer  zone  R. 

Analysis  of  a  plate  with  a  tapering  inner  zone  like  that  shown 
in  Fig.  144  gave  the  values: 


SAMPLING  OF  IRON  AND  STEEL 


431 


TABLE  XXII 


Samples  taken 

Phosphorus, 
per  cent 

Sulfur, 
per  cent 

By  planing  over  the  whole  cross-section  at  "a" 
(Fig.  96),  i.e.,  only  from  the  outer  zone  
Planing  over  the  section  to  include  both  outer 
and  inner  zones 

0.048 
0  085 

0.033 
Not 
determined 

From  the  inner  zone,  K  

0.110 

0.101 

432 


MICROSCOPIC  EXAMINATION  OF  METALS 


To  avoid  mistakes  of  this  sort  in  sampling  iron  or  steel  plates, 
not  only  for  chemical  but  for  metallographic  work,  the  planings 
or  section  should  be  taken,  not  at  the  edges  of  the  plate  a-a  or 
b-b  in  Fig.  145  but  at  c-c  or  d-d. 

a d  Wrought  Iron. — The  same  general 

rules  for  getting  average  samples 
from  wrought  iron  hold,  as  in  the  case 
of  ingots  and  steel.  Whenever  it  is 
possible,  the  shavings  should  be  made 
by  planing  over  the  whole  cross- 
section.  As  wrought  iron  always 
contains  slag  which  is  often  present 
in  considerable  quantities,  special 
care  must  be  taken  in  collecting 
the  sample  as  it  comes  from  the 
planer,  because  of  the  fact  that  the  siliceous  slag  is  reduced  to  a 
fine  powder  on  planing,  and  its  loss  would  seriously  affect  the 
analytical  results.  The  powdery  part  is  high  in  oxidic  com- 
pounds, also  rich  in  phosphorus  and  silicon.  For  results  which 
really  represent  the  composition  of  the  sample,  it  is  necessary  to 
weigh  the  shavings  and  the  powder  separately  and  combine 
them,  in  the  ratio  in  which  they  occur  in  the  original  sample, 
in  the  preparation  of  the  small  sample  for  analysis.  When  a 
wrought-iron  boiler  plate,  for  example,  was  sampled,  42  g.  of 
shavings  and  1.3  g.  of  powder  were  obtained.  Silicon  and 
phosphorus  determinations  gave  the  values: 

TABLE  XXIII 


FIG.   145. 


In  the  coarse 
part 

In  the  powder 

Silicon                 

0.06 

0.30 

Phosphorus  .  .  .  

0.23 

0.37 

It  is  evident,  then,  that  in  order  to  get  a  representative  sample 
for  analysis,  it  would  be  necessary  to  have  the  shavings  and 
powder  present  in  the  small  analytical  sample  in  the  ratio  of 
42:1.3,  or  about  32  times  as  much  metal  as  powder. 

In  the  case  of  puddled  iron,  the  differences  are  due  chiefly  to  the 


SAMPLING  OF  IRON  AND  STEEL 


433 


irregular  distribution  of  the  slag  and  the  presence,  therefore,  of 
phosphorus-,  silicon-  and  oxygen-rich  spots  in  the  product. 
Figure  146  is  the  cross-section  of  a  link  of  puddled  iron.  The 
very  dark  spots  in  different  parts  of  the  field  indicate  local  areas 
rich  in  phosphorus.  Analysis  gave: 


FIG.  146.— Puddled  iron. 
TABLE  XXIV 


Samples  taken 

Phosphorus, 
per  cent 

By  planing  over  the  cross-section  

0.17 

By  boring  in  the  dark  spots.  .    . 

0  30 

In  a  boiler  plate,  planing  over  the  section  showed  0.18  per 
cent  phosphorus,  while  borings  from  the  dark  spots  gave  0.29 
per  cent. 

Figures  147  and  148  show  etched  specimens  of  wrought  iron. 
The  fairly  uniform  distribution  of  the  dark  areas  over  the  entire 
surface  in  Fig.  147  indicates  a  high  average  phosphorus  content. 
Analysis  gave  0.25  per  cent. 

28 


434  MICROSCOPIC  EXAMINATION  OF  METALS 


FIG.  147. 


FIG.  148. 


SAMPLING  OF  IRON  AND  STEEL  435 

Figure  148  shows  that  in  this  case  the  areas  rich  in  phosphorus 
are  local.     The  values  found  were : 

TABLE  XXV 


Sample  taken 


Phosphorus, 
per  cent 


By  planing  over  the  whole  cross-section |  0 . 07 

By  boring  in  the  dark  streaks j  0.16 

These  illustrations  show  that,  in  the  same  specimen  of  wrought 
iron,  great  differences  of  composition  may  occur  in  different  parts 
of  the  cross-section  and  of  the  longitudinal  section.  In  contrast 
to  ingot  iron,  where  the  segregation  is  confined  as  a  rule  to 
definite,  and  sharply-marked  zones,  in  wrought  iron  segregated 
areas  are  irregularly  distributed  over  the  whole  surface  of  the 
section. 

To  obtain  even  an  approximately  representative  sample  of 
wrought  iron  it  is  necessary,  therefore,  to  take  samples  by  plan- 
ing over  the  entire  surface  of 'various  parts  of  the  piece  and  to 
unite  the  various  shavings.  The  necessity  of  collecting  the  fine 
powder  has  been  emphasized  already.  * 

In  wrought  iron,  the  third  significant  figure  is  valueless  in 
the  percentage  found  by  analysis  (even  for  phosphorus  and  sul- 
fur) because  of  the  variations  in  the  composition  of  the  original 
material. 

Sampling  of  Cast  and  Pig  Iron. — White  Iron. — Perfect  sampling 
of  white  iron  is  practically  impossible,  because  it  is  usually  too 
hard  to  plane  and  drilling  is  difficult  and  unsatisfactory.  Small 
castings  may  be  broken  to  pieces,  then  crushed  and  in  this  way 
a  representative  sample  made;  but  in  most  cases,  it  is  a  question 
of  sampling  a  casting  so  large  that  it  cannot  be  so  treated,  and  the 
sampler  must  knock  off  small  pieces  from  the  large  casting. 
Owing  to  the  abnormal  conditions  considered  on  p.  402  the  dif- 
ferent pieces  of  a  casting  may  differ  considerably  in  chemical 
composition.  Therefore  in  a  report  on  an  analysis  of  this  sort 
the  chemist  should  always  give  the  method  of  sampling  and,  in 
case  of  doubt,  should  state  specifically  that  the  analysis  may  not 
absolutely  represent  the  composition  of  the  casting  submitted  for 
analysis. 


436  MICROSCOPIC  EXAMINATION  OF  METALS 

Sampling  Gray  Iron. — One  of  the  most  difficult  problems  of 
the  steel  chemist  is  to  get  representative  samples  of  gray  iron. 
The  graphite  plates  distributed  through  the  material  make  it 
necessary  to  use  special  care  in  the  preparation  of  the  sample  for 
analysis  if  it  is  to  be  at  all  reliable. 

In  this  case  as  in  all  others  where  a  cutting  tool  can  be  used, 
the  whole  cross-section1  should  be  planed  down  to  get  an  average 
sample  for  analysis.  Borings  should  not  be  used. 

During  the  planing  and  collect- 
ing of  the  sample,  great  care  must 
be  taken  or  there  is  likely  to  be  a 
large  loss  of  graphite. 

For  the  analysis  of  a  single  piece, 
a  pig  for  example,  approximately 

equal  quantities  of  shavings  should  be  taken  from  different  places 
(marked  1,  2  and  3  in  Fig.  149)  and  then  combined  to  make  an 
average  sample. 

Shavings  from  dark  gray  iron  are  never  of  equal  size.  On 
planing,  a  coarse  part  I  and  a  finer  part  II  are  always  formed. 
The  finer  part  II  also  contains  the  graphite  plates  torn  out  by 
the  plane.  If  the  shavings  are  shaken  for  a  long  time  in  a  glass 
bottle,  it  is  usually  possible  to  separate  a  still  finer  part  which 
is  much  richer  in  carbon  than  either  of  the  other  two.  After 
the  sample  bottles  have  been  filled  with  the  shavings  and  allowed 
to  stand  for  some  time,  the  three  grades  of  material  separate  of 
their  own  accord.  The  coarsest  shavings  stay  at  the  top,  the 
next  coarser  are  below  in  the  bottle,  and  at  the  bottom  are  found 
the  finest  particles  which  are  rich  in  graphite. 

Even  if  the  contents  of  the  bottle  are  thoroughly  mixed,  it  is 
difficult  to  get  a  correct  average  sample  for  analysis.  For  exact 
work,  as  in  an  umpire  analysis,  it  is  always  necessary  in  this 
case  to  divide  the  sample  by  sifting  it  into  two  or  three  portions, 
each  part  to  have  material  of  the  same  size.  The  weight  of 
each  portion  is  then  taken  and,  the  final  sample  for  analysis  is  pre- 
pared by  mixing  together  some  of  each  sample  in  the  proper 
proportion  by  weight.  The  method  is  best  shown  by  the  follow- 
ing example. 

The  total  weight  of  shavings  made  by  the  plane  was  693  g. 

1  Exceptions  to  this  rule  will  be  mentioned  later. 


SAMPLING  OF  IRON  AND  STEEL 


437 


By  means  of  sieves  this  material  was  subdivided  into  parts  I, 
II  and  III 

I  coarse  part  =  a  grams  (469  g.) 

II  middle  size  =  0  grams  (193  g.) 

III  finest  part  =  7  grams    (31  g.) 

To  get  a  1-g.  sample  the  weighing  should  be  as  follows: 
Of     I  =  — -4n       =  0.6768g. 


a 


Of    II  = 


Of  III  = 


a+0 


a  +  0  +  7 


0.2785g. 


=  0.0447g. 


The  three  parts  should  then  be  combined  to  make  a  single  sample. 

The  brass  sieve  shown  in  Fig.  150  is  well  adapted  for  this  use. 
The  upper  cover  must  fit  tightly  in  order  to  avoid  any  possible 
loss  of  the  finest  part  as  dust.  Sieves  ^^ 

with   80   and  120  meshes  to  the  linear  YJjj 

inch  suffice  for  all  analytical  work. 

How  different  the  chemical  compo- 
sition of  the  different  parts  can  be, 
especially  in  the  percentage  of  total 
carbon  and  graphite,  is  shown  by  the 
following  examples. 

Example  1. —  From  a  square  bar  (130 
by  130  mm.)  of  dark  gray  cast  iron,  189  g. 
were  taken  by  planing  over  the  entire 
cross-section. 


After  sifting  through  an  80-mesh  sieve  FIG.  150.— Section  of  brass 
there  were  obtained:  sieve- 

173  g.  of  coarse  I 
16  g.  of  fine  II1 

1  Part  II  showed  a  distinct  tendency  to  separate  on  shaking.  The  shiny 
black  graphite  plates  collected  on  the  surface  and  were  readily  distinguished 
from  the  gray  iron.  A  second,  finer  sieve  ought  to  have  been  used  in  this 
case  because  the  separate  graphite  determinations  varied  from  12.64  to 
10.68,  a  deviation  which  could  only  be  due  to  segregation. 


438 


MICROSCOPIC  EXAMINATION  OF  METALS 


The  analyses  are  given  in  the  following  table : 

TABLE  XXVI. — DARK  GRAY  CAST  IRON 


I 
In 
coarse  part, 
per  cent 

II 

In 
fine  part, 
per  cent 

Average  composition1 
of  sample  as  calcu- 
lated from  I  and  II, 
per  cent 

Total  carbon  

2.62 

11.66 

3.39 

Graphite  
Combined  carbon  

2.38 
0.24 

10.91 
0.75 

3.10 
0.29 

Silicon  
Phosphorus  
Sulfur 

2.44 
0.51 
0  08 

2.27 
0.56 
0  073 

2.42 
0.515 
0  079 

Example  2. — The  differences  are  even  more  clearly  shown 
in  this  second  case  in  which  three  parts  were  separated.  Plan- 
ing over  the  cross-section  of  a  pig  of  Swedish  gray  iron  gave  696  g. 
of  shavings.  After  passing  through  an  80-  and  a  120-mesh 
sieve  there  were  obtained: 

I  =  469  g.  coarse  particles 
II  =  193  g.  medium  particles 
III  =    31  g.  fine  particles 
Analysis  of  the  three  parts  gave: 

TABLE  XXVII. — DARK  GRAY  IRON 


I 

II 

III 

Average  composi- 

In coarse 

In  medium 

In  fine 

tion  of  the  pig 
as  calculated 

part, 
per  cent 

part, 
per  cent 

part, 
per  cent 

from  I,     II  and 
III,  percent 

Total  carbon  

3.53 

4.04 

22.00 

4.50 

Graphite  

2.12 

2.53 

20.94 

3.07 

Combined  carbon  

1.41 

1.51 

1.06 

1.43 

Silicon  

0.81 

0.83 

0.76                          0.80 

Phosphorus  

0.051 

0.044 

0.03                          0.048 

Sulfur  

0.017 

0.014 

0.013                        0.016 

1  The  method  of  calculation  is: 

al  +  611 

I  +H 

where  a  is  the  per  cent  found  in  part  I  and  b  the  per  cent  found  in  part  II. 
For  the  calculation,  then,  of  total  carbon  in  the  table, 
2.62X173+11.66X16 


189 


=  3.39  per  cent. 


SAMPLING  OF  IRON  AND  STEEL 


439 


The  differences  in  the  graphite  and  total  carbon  content 
are  considerably  greater  in  this  case  than  in  the  former  one. 

Finally  the  total  carbon  and  graphite  were  determined  in  a 
1-g.  sample  (taken  with  reference  to  the  weight  of  the  separate 
parts  as  explained  on  p.  60).  The  values  found  were: 

Total  carbon 4 . 43  per  cent 

Graphite 3 . 03  per  cent 

Calculated  combined  carbon 1 . 40  per  cent 

These  values  agree  well  with  the  results  calculated  in  Table 
XXVI.  These  studies  show  that  in  working  with  iron  which  is 
rich  in  graphite,  the  analyst  must  take  every  possible  precaution 
not  only  in  taking  the  sample  but  also  in  the  final  weighing; 
otherwise  incorrect  results  are  likely  to  be  obtained. 

Inequalities  in  the  Chemical  Composition  of  Gray  Iron. — If 
the  shavings  to  be  used  for  the  average  analysis  are  taken  from  a 
single  place  instead  of  from  the  whole  cross-section,  the  inequali- 
ties in  the  composition  of  the  casting  have  an  effect  upon  results 
obtained  by  analysis.  Sampling  by  boring  is  also  unsatis- 
factory if  an  accurate  average  analysis  is  to  be  made,  for  with 
heterogeneous  material  the  sample  can  be  affected  materially 
by  the  depth  of  the  boring.  The  following  example  shows  that 
very  considerable  differences  in  com- 
position may  exist  between  different 
points  on  the  cross-section. 

Borings  were  taken  from  a  pig  of 
basic  Bessemer  iron  at  points  20  mm. 
apart  as  shown  in  Fig.  151.  Determi- 
nations of  manganese  and  phosphorus 
in  the  borings  gave  the  values  shown 
in  Table  XXVIII.1 

The  percentage  of  manganese  and  of  phosphorus  is  different 
at  each  point  on  the  surface  of  the  pig. 

Three  pigs  I,  II  and  III  were  taken,  the  first  from  one 
end  of  the  bed,  the  second  from  the  middle  and  the  third 
from  the  other  end  of  the  bed.  Three  samples  were  taken 
from  each  pig,  at  the  points  marked  0,  M  and  U  in  Fig.  152. 


FIG.  151. 


1  From  C.  Reinhardt,  Repertorium  d.  anal.  Chem.,  49,  744. 


440  MICROSCOPIC  EXAMINATION  OF  METALS 

TABLE  XXVIII 


Sample  taken  at 

Manganese 

Phosphorus 

a 

3.42 

2.91 

b 

3.11 

2.41 

c 

3.22 

2.65 

d 

3.11 

2.58 

e 

3.06 

2.39 

f 

3.17 

2.65 

Tabary1  found  the  percentages  of  total  carbon  as  follows: 


TABLE  XXIX 


Total  carbon  in  pig 


Borings  taken  at 

I 

Per  cent 

II 

Per  cent 

HI 

Per  cent 

0  —  top  .  . 

3  53 

3  55 

3   44 

M  —  center 

3  55 

3  72 

3  55 

U  —  bottom  

3.01 

3.44 

3.40 

FIG.  152. 


The  percentage  of  carbon  is  greatest  in  the 
center  and  least  at  the  bottom  of  the  pig. 

Sampling  in  Special  Cases. — In  addition  to 
the  unintentional  irregularities  in  the  compo- 
sition of  a  sample  of  steel  or  iron,  which  are  due 
to  segregation,  decarbonization,  excrescences 
on  cast-iron  and  the  like,  local  changes  are 
sometimes  produced  intentionally  during  the 
process  of  manufacture.  The  commonest  illustration  of  this 
sort  of  local  change  is  that  produced  by  the  operation  of  case- 
hardening  where  the  outer  layer  becomes  much  richer  in  carbon 
than  the  soft  steel  core.  In  a  case  of  this  kind,  an  average 
analysis,  for  which  samples  are  obtained  by  planing  over  the 
entire  cross-section,  is  of  little  value.  The  important  question 
is  to  determine  how  much  carbon  has  been  taken  up  and  the 
1  P.  TABARY,  Stahl  u.  Eisen,  1894,  1075. 


SAMPLING  OF  IRON  AND  STEEL  441 

depth  of  the  carbon-rich  zone.  In  this  case  the  metallographic 
examination  should  always  precede  the  chemical  analysis.  (See 
p.  395.) 

Frequently  the  piece  is  quenched  from  red  heat  after  its 
exposure  to  the  case-hardening  material.  The  outer  layer,  rich 
in  carbon,  becomes  hard  while  the  inner  core  remains  soft.  If 
such  a  hardened  piece  is  to  be  analyzed,  it  must  be  annealed  in 
order  to  make  it  possible  to  take  the  sample.  Special  care  must 
be  taken  during  the  annealing  not  to  lose  carbon  by  superficial 
oxidation.  The  precautions  to  be  taken  have  been  described 
on  p.  425.  Care  must  be  taken,  also,  to  avoid  a  transfer  of 
carbon  from  the  richer  outer  layer  to  the  interior.  The  annealing 
time,  therefore,  is  made  as  short  as  possible  (about  J^  nrO  and 
the  annealing  temperature  is  also  kept  as  low  as  possible  (750 
to  800°C.).  If  the  specimen  in  question  is  ordinary  carbon 
steel  (not  a  special  steel),  it  may  be  quenched  in  water  after  the 
furnace  temperature  has  fallen  below  700°C.  since  hardening  does 
not  take  place  below  the  pearlite  point.  If  these  precautions 
are  taken  during  the  annealing,  the  transfer  of  carbon  is  very 
slight. 

Magnetic  Testing  and  X-ray  Examination  of  Steel. — A  dis- 
cussion of  the  methods  of  testing  steel  would  not  be  complete 
without  a  brief  reference  to  two  modern  aids  to  the  metal  in- 
spector, the  magnetic  testing  device  and  the  x-ray  study  of 
metals  for  the  purpose  of  detecting  blow  holes,  slag  inclosures 
and  similar  defective  areas.  Neither  method  is  fully  developed 
at  the  present  time  but  in  certain  cases  the  methods  will  give 
results  of  the  greatest  practical  value  which  can  be  obtained 
in  no  other  way.  Both  methods  have  the  added  advantage  that 
each  may  be  used  without  injuring  in  any  way  the  material 
under  examination. 

The  possibility  of  making  use  of  the  magnetic  properties  of 
metals  as  a  means  of  determining  their  mechanical  properties 
has  been  a  subject  of  discussion  and  careful  experiment  for  many 
years.  Investigation  of  the  problem,  as  it  is  applied  to  the 
detection  of  heterogeneous  material,  has  been  carried  out  for  a 
number  of  years  under  the  direction  of  Dr.  Charles  W.  Burrows 
of  the  magnetic  section  of  the  Bureau  of  Standards.  Mr.  Frank 
P.  Fahy  of  the  Pennsylvania  Railroad  had  also  been  investi- 


442  MICROSCOPIC  EXAMINATION  OF  METALS 

gating  the  problem,  and  in  1911  the  two  investigations  were 
combined  and  have  continued  since  that  time.  Through  the 
efforts  of  these  men  and  with  the  active  cooperation  of  other 
investigators  many  of  the  practical  difficulties  have  been  over- 
come and  instruments  have  been  devised  which  make  the  method 
of  magnetic  testing  of  very  great  value  in  special  cases.1 

The  main  problem  of  magnetic  analysis  is  the  correlation  of  the 
magnetic  and  mechanical  properties  of  steel.2  Various  magnetic 
characteristics  have  been  studied  in  this  connection,  but  the  one 
most  commonly  used  is  permeability,  the  ratio  between  magnetic 
induction  and  the  magnetizing  force.  For  the  determina- 
tion of  permeability  Fahy5  has  devised  an  extremely  sensitive 
permeameter. 

Two  phases  of  magnetic  testing  have  to  be  considered,  first,  a 
study  of  the  average  character  of  the  specimen  under  examination, 
whether  it  has  been  quenched,  annealed,  strained  or  otherwise 
altered;  and  second,  whether  a  specimen  of  some  length,  like  a 
steel  rail,  is  uniform  throughout  or  whether  it  contains  defects 
like  blow  holes,  slag  spots  and  the  like.  Both  of  these  needs 
have  been  combined  in  Burrows'  instrument,  the  Magnetic 
Analyzer,  which  is  so  arranged  that  the  magnetic  condition  of  the 
material  under  test  can  be  observed  on  a  translucent  scale  or  it 
can  be  recorded  photographically.  The  general  nature  of  the 
curves  obtained  is  shown  in  Fig.  153.  The  most  important 
problem  which  has  been  undertaken,  up  to  the  present  time,  is  the 
study  of  steel  rails  and  the  results  have  been  so  satisfactory  that 
the  method  has  been  adopted  as  a  standard  control  method  on  one 
of  the  large  railroads.  It  is  not  improbable  that  the  method 
may  be  so  modified  as  to  make  it  possible  to  study  rails  in  actual 
service,  permitting  their  removal  before  complete  fracture  occurs. 

Magnetic  analysis  has  also  been  applied  with  success  to  the 
testing  of  steel  wire,  strips  or  cable  which  can  be  pulled  through 

1  A  discussion  of  Magnetic  Analysis  is  given  in  the  Proceedings  of  the 
American  Society  for  Testing  Materials,  19,  (1919)  Part  II,  from  which  is  taken 
most  of  the  information  given  here  on  magnetic  testing.     A  description  of  the 
instruments  used  is  given  in  detail  in  Bull.  41  of  Holtz  and  Company,  New 
York. 

2  "Correlation  of  the   Magnetic  and   Mechanical  Properties  of  Steel," 
Scientific  Paper,  272,  U.  S.  Bureau  of  Standards. 

3  Chem.  and  Met.  Eng.,  19,  339  (1918). 


SAMPLING  OF  IRON  AND  STEEL 


443 


the  solenoid  coil  of  the  instrument  at  a  fairly  high  rate  of  speed. 
Marked  irregularities  in  the  magnetic  curve  indicate  inequalities 
or  more  serious  defects  in  the  material  under  test. 

X-ray  Examination  of  Defective  Metal. — The  metal  specimen 
to  be  examined  is  placed  in  contact  with  an  x-ray  plate,  and 
both  are  protected  against  interfering  rays  by  means  of  a  suitably 
arranged  lead  screen.  An  exposure  is  then  made  using  a  Coolidge 


nf  and   /v  *j fro  to  A  te/?ea/ 


Compressed  /n 


FIG.  153. — Magnetic  permeability  curves. 

tube  as  the  source  of  rays,  the  length  of  exposure  depending  on 
the  nature  of  the  material,  the  thickness  of  the  metal,  and  the 
voltage  of  the  current  used  to  produce  the  rays. 

The  method  has  been  used  chiefly  in  the  study  of  autogeneous 
welds  and  castings  suspected  to  contain  blow  holes,  Fig.  154. 
Up  to  the  present  time  it  has  been  applied  only  to  steel  specimens 
less  than  1 J^  in.  thick.  The  radiograph  shows  only  the  massive 
structure  of  the  metal,  and  gives  no  information  as  to  grain  size 


444  MICROSCOPIC  EXAMINATION  OF  METALS 

or  crystal  structure.  It  does,  however,  give  valuable  information 
as  to  the  presence  of  blow-holes,  slag  inclusions,  porous  spots 
and  similar  defects,  and  has  the  distinct  advantage  that  the 


FIG.  154. — X-ray  photograph  showing  blow  holes  in  steel.     (Davey.) 

test  does  not  involve  the  cutting  or  drilling  of  the  material. 
No  fluoroscopic  screen  which  is  sensitive  enough  to  make  possible 
the  visual  examination  of  metals  has  yet  been  developed  so  that, 


SAMPLING  OF  IRON  AND  STEEL  445 

at  the  present  time,  work  with  metals  must  be  done  by  means  of 
axray  photographs. 

The  method  is  expensive,  and  its  applications  are  limited  as 
yet,  but  in  those  cases  in  which  it  has  been  used  the  results  are 
of  great  value.1 

1  Information  concerning  metal  radiography  was  obtained  from  Dr.  W.  P. 
Davey  of  the  General  Electric  Company  by  whom  the  radiograph  Fig.  154 
was  taken. 


CHAPTER  XXIX 
THE  ALLOYS  OF  COPPER 

The  alloys  of  copper,  which  include  the  brasses,  bronzes, 
heavy  bearing-metals  and  the  like,  are  next  in  importance  from 
an  industrial  standpoint  to  iron  and  steel  and  with  them,  too, 
the  microscope  is  an  almost  indispensible  tool  for  the  metal 
tester.  Metallographic  examination  of  these  alloys  is  not  so 
important  as  it  is  in  the  case  of  iron  and  steel  from  the  view  point 
of  the  analyst  who  is  interested  in  getting  representative  samples, 
as  segregation  is  so  much  less  strongly  marked.  The  physical 
properties  of  the  copper  alloys  change  so  rapidly,  however,  when 
they  are  subjected  to  mechanical  work,  that  in  many  cases  the 
chemical  analysis  alone  will  give  no  information  at  all  as  to  the 
value  of  the  material  for  a  given  purpose.  In  a  few  cases  segrega- 
tion does  take  place  to  a  marked  degree,  and  sampling  without 
an  examination  of  the  specimen  is  of  no  value. 

Preparation  of  the  Specimens. — Several  conditions,  which 
will  be  considered  in  detail  later,  are  involved  in  the  study  of 
metals  which  have  been  worked,  and  each  case  may  need  a 
sample  of  a  different  kind.  There  are  many  articles  made  from 
brass,  for  example,  which  are  subjected  to  severe  strain  at  but 
one  point,  or  at  least  within  a  very  limited  area.  In  such  cases  it 
is  necessary  to  take  only  a  small  section  from  the  danger  point, 
to  determine  whether  or  not  the  material  is  safe  to  use.  On  the 
other  hand,  it  may  be  very  necessary  to  know  whether  or  not 
the  material  is  homogeneous  throughout  a  considerable  length, 
or  over  a  large  area.  In  such  a  case  a  large  specimen,  or  a 
number  of  small  specimens  at  different  points,  must  be  taken. 
This  lack  of  homogenity  is  illustrated  in  Fig.  155,  which  shows 
the  wide  variation  in  appearance  of  a  brass  shell-case  over  a 
comparatively  limited  area.  The  differences  in  the  physical 
properties  at  the  different  points  are  very  marked.  As  the 
specimen  shown  is  perfectly  homogeneous  chemically,  the  value 
of  microscopic  examination  is  obvious.  It  also  illustrates  the 

446 


THE  ALLOYS  OF  COPPER 


447 


necessity  of  a  careful  selection  of  the  metallographic  sample, 
when  it  is  known  that  the  material  has  been  subjected  to  unequal 
amounts  of  work  in  its  fabrication.  The  selection  of  the  sample, 
then,  is  one  which  cannot  be  made  wholly  at  random,  but  which 


FIG.  155. — Section  of  brass  shell  case.     10  X- 

requires  thought  on  the  part  of  the  sampler,  if  the  specimen 
examined  is  to  give  a  true  indication  of  the  character  of  the 
metal  of  which  it  is  a  part. 


448  MICROSCOPIC  EXAMINATION  OF  METALS 

Polishing. — After  a  specimen  of  suitable  shape  and  size  has 
been  selected  for  examination,  the  piece  is  filed  and  polished  in 
the  way  indicated  in  discussing  the  preparation  of  iron  and 
steel  specimens  (p.  338),  except  that  in  this  case,  the  grinding 
and  polishing  operation  can  usually  be  carried  out  with  a  smaller 
number  of  abrasive  papers.  For  common  brass  and  bronze 
pieces,  the  following  sequence  of  abrasives  will  do  the  work. 
Coarse  file,  fine  file,  French  emery  paper  (Marke  Hubert)  1C, 
0,  00,  30-min.  emery  in  suspension,  and  alumina  or  rouge  in 
suspension,  the  two  last  abrasives  being  used  on  rotating  disks. 
It  is  seldom  necessary  to  use  emery  paper  finer  than  00,  except 
with  very  soft  alloys  rich  in  lead  (the  plastic  bronzes)  with 
which  000  or  even  0000  emery  paper  is  needed  to  get  a 
satisfactory  surface.  If  these  fine  papers  are  used,  they  should 
be  kept  moist  with  light  machine  oil  during  the  polishing  opera- 
tion. The  copper  alloys  are  scratched  so  much  more  easily 
than  steel  or  iron  that  they  must  be  held  very  lightly  against  the 
rotating  disks  used  in  the  final  polishing  operation.  It  is  hardly 
necessary  to  say  that  even  greater  care  must  be  taken  with  these 
relatively  soft  specimens  to  avoid  the  transfer  of  coarse  abrasive 
to  a  surface  on  which  a  finer  powder  is  to  be  used. 

Etching  of  Brass  and  Bronze. — Numerous  etching  reagents 
have  been  used  for  these  alloys,  the  selection  depending  to  a 
large  extent  on  the  way  in  which  the  specimen  is  to  be  used. 

1.  Nitric  Acid. — Nitric  acid,  d.  1.2,  is  a  useful  reagent  for 
the  rapid  examination  of  the  specimen  at  low  magnifications 
(100  diameters  or  less).  It  develops  the  crystalline  struc- 
ture readily,  with  strong  contrasts  between  crystals  of  different 
shapes  and  sizes.  It  is  especially  useful  in  the  macroscopic  study 
of  large  specimens  which,  because  of  their  size,  cannot  be  polished 
as  perfectly  as  the  small  pieces  commonly  used.  The  chief 
objection  to  the  use  of  nitric  acid  is  that  it  has  a  tendency  to 
attack  the  crystal  boundaries  so  strongly  that  details  of  the  struc- 
ture are  wholly  lost.  Consequently  it  is  of  little  use  for  specimens 
which  are  to  be  examined  and  photographed  at  magnifications  of 
200X1  or  greater.  Nitric  acid  is  used  either  by  application  to  the 
specimen  with  a  swab  held  in  forceps,  or  by  immersion  of  the 
specimen.  The  latter  method  is  rather  easier  to  control,  but  in 

1  The  symbol  200x  is  used  to  indicate  a  magnification  of  200  diameters. 


THE  ALLOYS  OF  COPPER  449 

this  case  the  specimen  must  be  agitated  constantly  during  its 
immersion  in  the  acid,  or  the  gas  bubbles  must  be  removed  by 
means  of  a  brush.  Otherwise  uneven  attack  will  cause  an 
appearance  of  the  specimen  which  is  quite  misleading.  Where 
photographs  are  to  be  taken  at  5  or  10  diameters  this  acid  is 
probably  the  best  reagent. 

2.  Ammonium    persulfate,    (NH4)2S2O8,    in    strong    ammonia 
(1  g.  in  20  c.c.  NH4OH  d.  0.90)  is  often  used  to  identify  /3-brass 
(p.  454),  which  it  attacks  readily,  leaving  a-brass  (p.  454)  practi- 
cally unattacked. 

3.  Ferric  Chloride  solution,  made  by  dissolving  10  g.  of  ferric 
chloride  crystals  in  100  c.c.  of  alcohol,  is  an  excellent  reagent 
for  the  etching  of  arsenical  brass. 

4.  Alkaline  Hydrogen  Peroxide. — The   most  effective  reagent 
for  ordinary  brass,  and  for  most  copper  alloys,  is  a  solution  of 
hydrogen  peroxide  (H2O2)  made  alkaline  with  ammonium  hy- 
droxide.    The   ratio   of   peroxide   to   ammonium   hydroxide   is 
determined  by  the  composition  of  the  alloy  under  investigation, 
but  for  most  purposes  one  of  the  following  compositions  will  be 
found  satisfactory: 

Zinc  less  than  10  per  cent,  1  c.c.,  peroxide  to  2  c.c.,  ammonium  hydroxide. 
Zinc  from  10  to  30  per  cent,  1  c.c.,  peroxide  to  5  c.c.,  ammonium  hydroxide. 
Zinc  from  30  to  40  per  cent,  1  c.c.,  peroxide  to  10  c.c.,  ammonium  hydroxide. 

(These  proportions  are  only  suggestive  for  the  concentration  of  the 
peroxide  solution  changes  rapidly  on  standing  and  the  best 
proportion  should  be  determined  by  trial.) 

It  is  of  the  greatest  importance,  in  the  application  of  this 
solution  that  it  should  be  made  from  fresh  and  strong  reagents, 
immediately  before  use.  The  chief  cause  for  failure  is  in  the  use 
of  material  which  has  been  allowed  to  stand.  The  method  of 
using  alkaline  peroxide  is  as  follows.  Hold  the  specimen  to  be 
etched  under  running  water  until  the  surface  is  thoroughly  wet, 
then  apply  the  reagent  by  means  of  a  swab  of  soft  cotton  and  rub 
the  surface  vigorously  for  a  few  seconds.  Hold  the  specimen 
under  the  tap  until  the  reagent  has  been  removed,  and  again 
apply  the  peroxide.  Repeat  these  operations,  of  rubbing  with 
the  etching  reagent  and  flushing  with  water,  until  the  desired 
amount  of  etching  has  been  done.  If  the  operation  has  been 

29 


450  MICROSCOPIC  EXAMINATION  OF  METALS 

carried  on  successfully  with  suitable  reagent,  the  surface  of  the 
brass  or  bronze  should  show  a  perfect  development  of  the  crystal- 
line structure  of  the  metal,  and  details  of  the  crystal  formation 
should  be  clearly  marked.  The  operation  of  etching  should  not 
take  more  than  5  min.  Dark,  over-etched  surfaces,  where  the 
detail  of  the  structure  is  obscured  by  thick  boundary  lines 
between  crystals  and  frequently  by  black  irregular  patches  over 
the  entire  surface  of  the  specimen,  are  usually  due  to  an  excess 
of  ammonium  hydroxide.  The  surface  may  be  cleared  and  the 
true  structure  developed,  in  a  case  of  this  kind,  by  using  a  fresh 
mixture  of  reagents  in  which  the  peroxide  is  present  in  a  slightly 
greater  quantity  than  would  normally  be  used.  Light  colored 
surfaces,  in  which  little  or  no  detail  of  the  structure  is  visible, 
are  usually  due  to  an  excess  of  peroxide  in  the  etching  liquid. 
The  difficulty  may  be  overcome  by  the  addition  of  strong  ammo- 
nium hydroxide  to  the  reagent.  In  a  few  cases,  however, 
the  lack  of  detail  in  the  structure  is  due  to  overstrained 
metal.  Brass  or  bronze  may  be  so  severely  overstrained  by 
mechanical  work  that  the  development  of  a  definite  crystal 
structure  is  very  difficult.  In  most  cases  of  this  kind,  it  will  be 
possible  to  recognize  the  crushed  cyrstal  masses  at  some  part  of 
the  surface  under  inspection,  so  that  the  reason  for  the  lack  of 
development  will  be  evident. 

Alkaline  hydrogen  peroxide  reacts  differently  from  the  persul- 
fate  mixture;  with  the  former  the  a-brass  (p. 453)  is  colored  yellow 
or  brown  and  /3-brass  (p.  454)  is  almost  unaffected,  while  with 
the  persulfate,  /3-brass  is  the  constituent  attacked. 

Copper  and  Its  Alloys. — In  addition  to  pure  copper,  which  is 
often  submitted  to  the  chemist  for  examination,  the  alloys  most 
commonly  encountered  are  those  of  copper  with  zinc  (the  brasses) 
and  those  of  copper  with  tin  (the  bronzes).  Many  possible 
alloys  may  be  made  of  the  bronze  type  or  of  the  brass  type, 
but  the  detection  of  slight  differences  of  composition  is  a 
problem  for  the  chemist,  not  for  the  metallographer.  Zinc,  in 
small  amounts,  is  often  added  to  tin-bronze  to  make  the  molten 
metal  more  fluid  for  casting  purposes.  Conversely  one  or  more 
per  cent  of  tin  is  often  added  to  certain  of  the  copper-zinc  alloys 
to  make  them  more  resistant  to  corrosion.  Arsenic,  antimony, 
bismuth,  iron  and  other  elements  in  small  quantity  are  often 


THE  ALLOYS  OF  COPPER 


451 


found  in  brass  or  bronze,  because  of  impurities  in  the  ores  from 
which  the  alloying  metals  were  originally  made.  These  elements, 
whether  added  inten- 
tionally or  present  as 
impurities,  are  of  very 
real  importance  to  the 
metal  tester,  but  can 
be  determined  at  pres- 
ent only  by  accurate 
chemical  analysis.  In 
brass  and  bronze  lead  is 
the  only  common  for- 
eign element  whose  pres- 
ence can  be  readily 
detected  by  the  micro- 
scope. It  is  frequently 
added  to  these  alloys 
with  the  idea  of  improv- 
ing the  machining  quali- 
ties of  the  metal,  and  is  visible  under  the  microscope  in  the  form 
of  more  or  less  circular  spots,  the  cross-sections  of  the  drops  in 

which  the  lead  is  present  in 


Fio.  156. — Unetched  bronze  showing  lead  drops. 
75  X. 


the  alloy.  Lead  is  more 
readily  seen  in  the  unetched 
specimen,  and  the  micro- 
scope tells  whether  it  is  uni- 
formly distributed  throughout 
the  metal  mass  in  which  it 

4        ^  C^^fe^^H    occurs.     Figure  156  shows  the 

T      ^  ^^^B      fairly  regular   distribution  of 

A    ^*      ^* *  lead  drops  through  a  sample 

^       ***  _     §rf[        *|    of  bronze,  and  Fig.   157  is  a 

bearing  metal  in  which  marked 
irregularities  in  the  distribu- 

157.— irregular   distribution   of    tion  of  the  lead  are  evident. 

Plastic  bronze,  which  is  made 
by  cooling  an  emulsion  of 
molten  lead  and  molten  copper,  two  elements  which  do  not 
mix  even  in  the  liquid  condition,  often  contains  50  per  cent  of 


FIG. 

lead   in  defective  plastic  bronze. 
(Homerberg.) 


75  X. 


452 


MICROSCOPIC  EXAMINATION  OF  METALS 


lead.  If  it  is  to  be  of  service  in  heavy  bearings  this  lead  should 
be  distributed  as  uniformly  as  possible  throughout  the  copper 
matrix.  The  microscope  gives  the  best  possible  means  of  deter- 
mining whether  or  not  the  plastic  bronze  was  correctly  made. 

The  chief  uses  of  the  microscope  in  connection  with  the  brasses 
and  bronzes  are  these:  (1)  To  determine  whether  the  metals  of 
which  the  alloy  was  made  have  been  uniformly  mixed,  a  question 
which  is  of  great  importance  in  dealing  with  those  alloys  which 
have  a  duplex  structure.  (2)  To  determine  the  character, 
,8 


Composition 
FIG.   158. — Copper-zinc  diagram.      (Shepard.) 

amount  and  distribution  of  the  non-metallic  impurities  (p.  456). 
(3)  To  determine  the  amount  and  nature  of  the  work  done  on  the 
alloy,  and  to  study  the  effects  which  may  have  been  produced  by 
annealing.  This  last  function  of  the  microscope  in  the  testing 
of  copper  and  its  alloys  is  by  far  the  most  important  as  it  makes 
it  possible  to  find  in  the  properties  of  the  metal  differences  of 
which  the  chemical  analysis  would  not  give  the  slightest  suggestion. 
To  come  back  to  the  question  of  uniform  mixing  of  the  alloy, 
it  is  evident  that  one  of  the  best  indications  of  lack  of  uniformity 
is  to  find  microscopic  evidence  of  a  duplex  structure  when  but  one 
crystal  form  should  be  found,  or  conversely,  to  find  but  a  single 


THE  ALLOYS  OF  COPPER 


453 


crystal  form  in  a  given  area  when  two  forms  ought  to  be  present. 
The  metal  tester  must  know,  then,  whether  a  single  crystal  type 
or  a  duplex  structure  is  to  be  expected.  This  information  is 
most  easily  found  by  reference  to  the  equilibrium  diagrams, 
Figs.  158  and  159.  These  diagrams  are  read  in  the  same 
way  as  the  steel  diagram,  p.  356,  and  give  to  the  metal  tester 
the  needed  information  as  to  the  general  character  of  the  alloy 


Composition 
FIG.  159. — Copper-tin  diagram. 

under  inspection.  The  application  of  these  diagrams  to  concrete 
cases  may  be  illustrated  by  a  few  examples.  In  Fig.  158,  which 
refers  to  the  alloys  of  copper  and  zinc,  it  will  be  seen  that  an  alloy 
containing  30  per  cent  of  zinc  (or  any  other  alloy  containing  less 
than  about  35  per  cent  of  zinc)  will  be  found  in  that  section  of  the 
diagram  marked  a  and  ought,  therefore,  to  be  a  perfectly  homo- 
geneous solid  solution,  and  should  show  but  one  kind  of  crystal 


454 


MICROSCOPIC  EXAMINATION  OF  METALS 


•y. 


r*4> 


I*: 


<*  t 


under  the  microscope.     Cast  brass  usually  cools  off  too  quickly  to 
allow  time  for  the  formation  of  perfectly  uniform  crystals  so  that 

it  commonly  has  the 
appearance  shown  in 
Fig.  160  in  which  the 
dark  worm-like  masses 
are  parts  of  the  crystal 
slightly  richer  in  copper 
than  the  major  portion 

jj.**     -:      — ***•  ?    *"-**ju  *  ^  ^,  Ji    *g'i    of  the  mass.     Very  slow 
f  .'VV    5  *****      "    *l   %      cooling  from  the  molten 

-  f'{%  condition  or  annealing  of 

/*!»4*J|*^  ^ne  solid  mass  will  cause 

a  diffusion  of  the  copper 

in  the    solid    metal   with 

*. -o  ^   w        ^ 

-V,.li^ 

FIG.   160.— Cast  a-brass.     75  X. 


<* 

V  4 


*•"»  e 

?:  ••'  % 


the  formation  of  the  uni- 
form crystal  shown  in  Fig. 
161.  The  copper-zinc 
alloys  in  this  range  (from  about  5  to  approximately  35  per  cent 
zinc),  usually  known  as  the  a-brasses  from  their  relation  to  the 

diagram,    are    the    most   im-       .  

portant  of  the  brass  alloys. 
The  a-brass,  containing  30 
per  cent  of  zinc,  often  called 
70-30  brass,  is  perhaps  the 
most  important  of  all  the 
copper  alloys.  The  succeed- 
ing areas  on  the  diagram  are 
not  so  sharply  defined  as  the 
ot-section,  but  under  normal 
conditions  a-  and  /3-brass  may 
be  expected  in  the  range  be- 
tween 64  and  58  per  cent 
copper,  with  pure  /3-brass 
in  the  range  between  58  and 
50  per  cent  of  copper.  The 
diagram  indicates  another  fact  of  importance  to  the  metal 
tester  who  is  interested  in  the  history  of  the  metal  under  exami- 
nation, namely  that  all  alloys  beyond  the  a-range  are  composed  of 


FIG.  161.— Solid  solution  of  zinc  in 
copper.  (Dark  spots  are  lead.)  75  X- 
(Homerberg.) 


THE  ALLOYS  OF  COPPER 


455 


two  elements  a  and  0,  or  a  and  7  if  the  melted  metal  is  slowly 

cooled.     It  also  shows  that  homogeneous  /3-brass  is  found  only 

in    the    triangular    area 

above   460°C.,    between 

approximately    50    and 

60  per  cent  of  copper. 

The    microscope    would 

show    but  one   kind    of 

crystal  if  the  alloy  was 

examined  at  the  higher 

temperature    or,    which 

is  the  usual  case,  if  the 

alloy  had  been  quenched 

from  some  temperature 

above     that    at    which 

pure    j8-brass    ceases   to 

exist.    Figure  162  shows 

a       Section      of       Muntz         FIG-  162. — Muntz  metal  annealed  at  750°  and 
mptfll      (rnnnpr     fiO     npr     <Juenched-     Chiefly  0-brass.     75   X-      (Johnson 

etai    (^  copper    ou    pe     and  jermain.) 

cent,  zinc  40  per  cent) 

which  has  been  cooled  quickly  from  750°C.,  and  should,  in 

accordance  with  the  di- 
agram, be  homogeneous. 
This  specimen  appears 
to  be  fairly  homogene- 
ous. The  small  amount 
of  a  second  type  of 
crystal  indicated  by  the 
dark  dots  is  due  to  the 
fact  that  the  cooling  was 
not  fast  enough  to  over- 
come wholly  the  ten- 
dency for  the  alloy  to 
separate  into  its  two 
compononents,  as  it 
would  have  done  on  slow 

FIG.  163.— Cast  Muntz  metal.     150  X.  Cooling,    as   is   shown   in 

Fig.    163,    an    alloy   of 

identical  composition  cast  in  the  ordinary  way  and  allowed  to 
cool  slowly. 


456  MICROSCOPIC  EXAMINATION  OF  METALS 

These  illustrations  from  the  a-  and  the  0-brass  sections  of  the 
diagram  serve  to  illustrate  the  way  in  which  the  diagram  may  be 
applied  in  technical  work  and  also,  the  sort  of  information  that 
the  microscope  will  give  that  cannot  be  obtained  by  chemical 
methods. 

Fortunately  for  the  metallographer  and  the  metal  tester,  the 
copper-zinc  alloys  in  which  the  percentage  of  zinc  is  greater  than 
50  are  so  brittle  that  they  are  never  used  for  purposes  in  which  the 
strength  of  the  material  is  a  factor,  so  that  for  practical  purposes 
the  a-  and  0-forms  are  the  only  ones  which  need  be  studied. 

The  bronze  diagram  (copper-tin)  is  even  more  complex  than 
that  of  the  copper-zinc  alloys,  but  in  this  case,  too,  the  alloys 
containing  more  than  25  per  cent  of  tin  are  too  brittle  for  indus- 
trial purposes,  except  in  the  making  of  decorative  castings. 
Therefore,  as  the  diagram  indicates,  the  inspector  has  to  deal 
only  with  the  a-  and  /3-forms,  as  with  the  zinc  alloys.  In  this 
case,  too,  the  diagram  indicates  that  homogeneous  0-bronze 
exists  only  in  a  very  limited  area,  in  the  temperature  range 
between  about  500  and  800°C.,  and  when  the  composition  is  from 
75  to  80  per  cent  copper:  Again  the  microscope  is  of  service,  for 
the  detection  of  an  homogeneous  specimen  of  bronze  of  this 
composition  would  indicate  positively  that  the  metal  had  been 
quenched  from  the  higher  temperature. 

When  bronze  is  cast  from  the  molten  state,  it  hardens  so 
much  more  rapidly  than  ordinary  brass  that  there  is  not  time 
enough  for  as  complete  an  equalizing  of  the  composition  of  the 
a-crystals.  The  result  is  that  the  etched  section  of  the  bronzes, 
whether  ordinary  tin  bronze,  or  phosphor  or  silicon  bronze, 
commonly  shows  the  characteristic  dendritic  structure  illustrated 
Fig.  164. 

The  second  important  application  of  the  microscope  to  the 
copper  alloys  is  in  the  study  of  the  non-metallic  inclusions, 
which  are  sometimes  present  and  are  so  difficult  to  detect  by 
chemical  methods.  Copper  and  its  alloys  which  have  been 
"burned,"  or  from  which  the  oxygen  has  not  been  sufficiently 
removed  by  phosphorus,  magnesium,  boron  or  other  deoxidizing 
agent  in  the  process  of  manufacture,  contain  varying  amounts 
of  copper  oxide,  which  forms  a  eutectic  mixture  with  copper 
and  may  have  an  extremely  harmful  effect  on  the  properties  of 


THE  ALLOYS  OF  COPPER 


457 


the  metal.  The  oxide  has  no  strength  or  ductility,  and  is  a  very 
real  source  of  weakness  if  it  is  present  in  any  appreciable  amount. 
It  is  especially  harmful  if  the  copper  or  bronze  is  to  be  made  into 


FIG.  164. — Dendritic  structure  of  cast  phosphor  bronze.     75  X. 

electrical  apparatus,  as  the  presence  of  even  a  minute  amount 
of  the  oxide  will  cause  a  sharp  decrease  in  the  conductivity  of 


FIG.  165. — Copper  oxide  eutectic  in 
copper.     100  X.     (Fay.) 


FIG.    166. — Slag  areas  in  defective 
brass  tube.     75  X- 


the  metal.  The  appearance  of  the  copper  oxide  eutectic  as  it 
is  found  in  bad  cases  is  shown  in  Fig.  165  and  of  inclosed  slag  in 
Fig.  166. 


458  MICROSCOPIC  EXAMINATION  OF  METALS 

Other  non-metallic  impurities,  which  occur  much  less  fre- 
quently in  non-ferrous  alloys  than  in  iron  and  steel,  have  been 
described.1 

The  Study  of  Worked  Material.— The  third,  and  far  the  most 
important  application  of  the  microscope  to  the  study  of  the 
brasses  and  bronzes,  is  in  the  examination  of  material  which  has 
been  subjected  to  mechanical  work,  rolling,  drawing,  hammering 
or  the  like  and,  as  a  corollary  to  this,  in  the  study  of  metal  which 
has  been  annealed  after  the  cold  work  has  been  done. 

If  a  metal  is  subjected  to  a  moderate  amount  of  cold  work,  such 
that  its  elastic  limit  is  not  exceeded,  no  change  in  its  structure 
will  be  noticed  under  the  microscope,  but  a  very  slight  increase 
above  the  elastic  limit  causes  a  change  in  the  structure  which  is 
evident  at  once.  A  highly  polished  specimen  which  is  subjected 
to  tension  while  it  is  in  position  under  the  microscope,  begins  to 


A.   Before  straining  _g   After  straining 

FIG.  167. — Sketch  showing  the  way  in  which  slip  bands  are  produced  in  strained 
metal.     (Rosenhain.) 

show  a  small  number  of  black  lines  as  soon  as  the  elastic  limit 
has  been  passed.  These  lines  are  practically  parallel  on  any  one 
crystal,  but  their  direction  varies  in  adjacent  crystals.  They 
do  not  cross  crystal  boundaries,  and  are,  therefore,  due  to  a 
change  in  the  individual  crystals  rather  than  in  the  entire  mass 
of  metal.  As  .the  amount  of  strain  increases,  these  parallel  lines 
become  more  numerous  until,  at  a  point  just  before  the  material 
breaks  or  crushes,  the  entire  surface  is  covered  with  a  mass  of 
of  lines,  giving  to  the  material  a  distinctly  fibrous  appearance 
under  the  microscope.  The  most  commonly  accepted  theory 
to  account  for  these  changes  is  that  the  very  small  layers,  of 
which  the  larger  crystal  grain  is  composed,  actually  slip  on 
each  other  so  that  the  surface  of  the  polished  specimen  is  no 
longer  smooth  but  corrugated,  as  indicated  in  the  sketch,  Fig. 

1  COMSTOCK,  J.  Am,  Inst.  Metals,  March  1918.     CARPENTER  and  ELAM, 
J.  Inst.  Metals  (British)  19,  155  (1919). 


THE  ALLOYS  OF  COPPER  459 

167,  the  number  of  ridges  increasing  with  the  amount  of  strain  to 
which  the  metal  has  been  subjected.  The  dark  lines  are  due 
to  the  fact  that  the  light  coming  through  the  microscope  tube 
is  not  reflected  back  into  the  tube  from  all  parts  of  the  surface, 
but  that  part  of  it  is  reflected  out  of  the  field  of  vision  when  it 
strikes  the  inclined  surfaces  of  the  ridges  formed  by  the  slip. 
Rosenhain  has  called  these  dark  lines  "slip  bands,"  and  the  term 
has  come  into  general  use. 

Another  phenomenon,  closely  allied  to  the  formation  of  slip 
bands,  is  the  production  of  what  has  been  called  "amorphous 
cementing  material ' '  along  the  planes  where  slipping  occurs.  The 
following  theory,  first  proposed  by  Beilby,  is  generally,  though 
by  no  means  universally,  accepted.  The  assumption,  for  which 
much  experimental  evidence  has  been  produced,  is  that  when  the 
crystal  planes  glide  or  slip  on  each  other,  a  small  amount  of 
material  is  produced  which  is  amorphous  in  character  and  is 
much  harder,  tougher  but  less  elastic  than  the  material  from 
which  it  is  formed.  As  the  amount  of  strain  increases  the  amount 
of  amorphous  material  also  increases,  and  those  properties  which 
are  characteristic  of  the  amorphous  material  become  more 
strongly  marked.  The  practical  effect  of  the  formation  of  this 
amorphous  cementing  material  is  well  known,  as  it  is  the  cause  of 
the  hardening  of  rolled  copper  sheets,  the  production  of  spring 
brass  wire  by  cold  work  and  other  operations  of  the  same  sort 
where  mechanical  work  greatly  increases  the  hardness  and  tensile 
strength  of  the  material.  The  amount  of  amorphous  material 
which  can  be  produed  safely  in  practice  is  limited  by  the  fact  that 
brittleness,  as  well  as  hardness,  accompanies  its  formation,  so 
that  if  the  metal  is  to  withstand  shock  the  amount  of  amorphous 
substances  must  be  carefully  controlled. 

Neither  slip  bands  nor  amorphous  material  can  be  seen  under 
the  microscope  when  the  specimen  is  polished  in  the  usual  way, 
but  both  effects  make  the  specimen  readily  susceptible  to  local 
etching  attacks  with  the  formation  of  characteristic  dark  lines 
and  bands  which  are  distinctly  visible  even  at  low  magnifica- 
tions. These  lines  or  bands  which  have  been  developed  by  the 
etching  of  a  strained  metal  are  often  known  as  "etch  bands," 
and  are  of  the  greatest  significance  to  the  metal  tester. 

The  fibrous  structure,  which  is  so  characteristic  of  badly  over- 


460 


MICROSCOPIC  EXAMINATION  OF  METALS 


FIG.   168. — a-brass  strained  and  not  annealed. 
75  X. 


strained  material,  is  shown  in  Fig.  168,  a  brass  tube  having  the 
composition  70  per  cent  Cu  and  30  per  cent  Zn.  It  is  a  remark- 
able fact,  and  one  which 
should  be  noted  by  the 
metal  inspector  that  a 
very  badly  strained  speci- 
men, like  the  one  shown 
in  the  figure,  is  much 
harder  to  etch  than  any 
other  type  of  brass  or 
bronze.  Long  etching 
with  fairly  strong  rea- 
gents is  needed  to  de- 
velop the  structure  at 
all,  and  the  contrast  be- 
tween the  different  parts 
of  the  crystal  is  so 
slight  that  satisfactory 
photographic  reproduc- 
tion is  practically  impossible.  The  fact  of  importance  to  the 
metal  tester,  then,  is  that  a  hard,  structureless  surface,  whose 
fibrous  character  is  shown 
only  by  severe  etching,  al- 
ways indicates  an  excessive 
amount  of  work  which  has  not 
been  relieved  by  annealing. 

Annealing .  —  The  brittle- 
ness  produced  by  cold  work  is 
so  harmful  in  most  cases  that 
it  is  necessary  to  soften  the 
material  by  the  operation  of 
annealing.  The  work  which 
is  done  in  the  shaping  of  a 
brass  or  bronze  piece  may  be 
unequally  distributed  over  the 
material,  and  so  may  cause 
brittleness  at  some  points 

and  not    at  others,   leading  to  a  condition    of   uneven   strain 
which  is   more   dangerous  than  uniform    brittleness.     In    this 


FIG.   169. — Fibrous  structure  and  crack 
in  strained  a-brass.     25  X. 


THE  ALLOYS  OF  COPPER 


461 


case,  annealing  is  used  not  merely  to  decrease  the  brittle- 
ness  of  the  material,  but  to  relieve  the  uneven  strain  produced 
by  the  cold  work.  Figures 
169  and  170,  sections  of  a 
brass  shell  case,  illustrate  the 
effect  of  cold  work  unevenly 
applied.  The  drawing  opera- 
tion was  of  such  a  character 
that  a  great  amount  of  work 
was  done  in  a  very  limited 
area,  leading  to  a  distinctly 
fibrous  structure  and,  at  the 
point  of  greatest  strain,  an 
actual  crack.  The  effect  of 
annealing  following  mechani- 
cal work  is  a  most  striking 

FIG.  170. — Badly  strained  a-brass. 

one,   and  gives  to  the  metal  75  x. 

tester  information  concerning 

the  heat  treatment  of  the  material  which  can  be  obtained  in  no 
other  way.  The  strained  or  crushed  material  begins  to  re- 
crystallize  when  a  moderate  increase  in  temperature  takes  place. 

The  recrystallization  is  ac- 
companied by  a  characteristic 
1  'twinning "  of  the  crystals 
which,  after  etching,  appear 
under  the  microscope  as  alter- 
nate light  and  dark  bands 
crossing  the  crystal  grain  but 
stopping,  as  do  the  slip  bands, 
at  the  grain  boundaries.  The 
first  step  in  the  recrystalli- 
zation takes  place  at  a  tem- 
perature which  depends  on 
the  amount  of  work  done  on 
the  material,  and  is  indi- 


FIG.   171. — Strained  a-brass  incom- 
pletely annealed.     75  X. 


cated    by    the  irregular   dis- 
tribution of  large  and  small 

crystal  masses   shown  in  Fig.   171.     A  structure  of  this  kind, 
which  is  formed  at  what  is  called  the  "  recrystallization  tern- 


462  MICROSCOPIC  EXAMINATION  OF  METALS 

perature,"  is  distinctly  undesirable  as  it  is  composed  of  large 
masses  of  the  hard,  unannealed  material  in  contact  with  the 
small  twin  crystals,  and  is  therefore  distinctly  heterogeneous. 
Although  the  chemical  analysis  might  be  good,  the  metallog- 
rapher  would  know  at  once  that  the  heat  treatment  had  not 
been  satisfactory,  and  would  condemn  the  material  if  it  were 
to  be  used  under  conditions  in  which  it  would  be  subjected  to 
shock. 

As  the  annealing  temperature  increases  the  twinning  becomes 
more  evident,  and  the  size  of  the  crystals  increases.  It  may  be 
said,  in  general,  that  the  higher  the  temperature  the  larger  the 
crystal  grains,  other  conditions  being  equal ;  but  it  is  also  true  that 
the  crystal  size  depends  to  an  extent  on  the  amount  of  work  done 
on  the  material  before  annealing.  Figure  172  shows  the  appear- 
ance of  cold-worked  and  annealed  brass  under  varying  conditions 
of  heat  treatment.  A  is  characteristic  of  severely  worked  brass 
which  has  been  annealed  at  a  temperature  slightly  above  its 
recrystallizing  temperature,  and  indicates  a  metal  which  is  hard, 
springy,  strong  and  not  very  ductile.  D,  on  the  other  hand, 
shows  a  forass  which  has  been  annealed  at  so  high  a  temperature 
that  it  is  practically  "  dead  soft,"  with  low  tensile  strength  and  no 
springiness  whatever.  Micrographs  B  and  C  represent  interme- 
diate conditions  in  which  either  the  amount  of  cold  work 
has  been  less  or  the  annealing  temperature  higher,  and  the 
resulting  metal  would  have  properties  intermediate  between  A 
and  D. 

The  question  of  grain  size  has  come  to  be  of  such  importance  in 
standardizing  materials  for  engineering  purposes  that  the  Amer- 
ican Society  for  Testing  Materials  has  adopted  certain  conven- 
tions that  will  be  of  great  service  in  unifying  micrographic 
practice  and  making  results  from  various  sources  truly 
comparable. 

Magnifications. — For  general  use  the  magnifications  shall  be 
10,  25,  50,  75,  100,  200,  500,  and  1,000  diameters. 


THE  ALLOYS  OF  COPPER 


463 


A.  Severely  cold  worked  cartridge  metal  be-       B.  Cold    worked    and    annealed.     Small    twin 
ginning  to  recrystallize.     75  X-  crystals  are  visible.     75  X- 


C.  Moderately  cold  worked  cartridge  metal  D.  Moderately  cold  worked  cartridge  brass 

after    annealing.     75  X.     (The    characteristic       annealed  at  700°C.     75  X.     (Large  twin  crys- 
twinned  structure  is  very  marked.)  tals  due  to  overheating.) 

FIG.   172. — Brass — 70  per  cent  copper,  30  per  cent  zinc. 


464  MICROSCOPIC  EXAMINATION  OF  METALS 

For    Showing  Grain   Size. — The  following  magnifications  are 
recommended : 

TABLE  XXIX 


Material 

Cast 

Wrought 

Steel  and  ferrous  materials  

100  diameters 

100  diameters 

Copper  

50  and  100  diameters 

75  diameters 

Copper-zinc  alloys  

50  and  100  diameters 

75  diameters 

Lead-tin-antimony  alloys 

50  and  200  diameters 

Grain  Size. — In  making  grain  size  measurements,  two  classes 
of  alloys  need  to  be  considered: 

1.  Alloys  consisting  of  but  one  type  of  crystal,  as  copper,  a-brass 
and  the  like  and 

2.  Alloys  consisting  of  two  or  more  metallographic  constituents 
like  the  steels,  Muntz  metal,  p.  454,  solder,  babbitt  metal,  p.  474, 
etc. 

If  an  alloy  of  the  first  class  happens  to  show  the  twinned 
structure,  the  original  crystal,  including  the  twinned  layers, 
is  always  called  one  grain.  In  an  alloy  of  the  second  class,  the 
original  grain  which  has  broken  down  into  the  two  components 
is  taken  as  the  unit,  if  it  can  be  determined,  or  if  the  decomposi- 
tion into  its  components  has  taken  place  in  such  a  way  as  to 
destroy  the  outlines  of  the  original  crystal,  the  individual 
component  is  taken  as  the  unit  of  measurement. 

Two  methods  of  measuring  grain  size  are  in  use,  depending  on 
the  condition  of  the  material  under  examination.  If  the  material 
has  grains  which  are  equi-axed  (axes  of  the  same  length),  as  is 
the  case  with  most  metals  which  have  been  cast  or  fully  annealed, 
a  method  based  on  the  number  of  grains  included  in  an  area  of 
definite  size  is  generally  used.  The  method  recommended  by 
Zay  Jeffries1  (p.  466)  is  simple  and  accurate.  Whatever  method 
of  grain  counting  is  used,  the  circular  area  should  always  include 
at  least  50  grains  in  order  that  an  average  measurement  may  be 
obtained. 

When  a  metal  has  been  strained  by  rolling,  hammering,  draw- 
ing or  a  similar  operation,  the  grains  are  no  longer  equi-axed, 
but  are  more  or  less  elongated  in  the  direction  in  which  the 

1  ZAY  JEFFRIES,  "  Grain  Size  Measurements,"  Met.  and  Chem.  Eng.,  18, 185. 


THE  ALLOYS  OF  COPPER 


465 


greatest  amount  of  strain  occurred  as,  for  example,  in  the  direct- 
ion of  rolling  or  drawing.     (Figs.  173  and  174.)     In  such  a  case 


^mJ$£S3BJk 

FIG.  173. — Moderately  worked  Muntz  metal  (Cu  60  per  cent-Zu  40  per  cent). 

75  X-     (O'Daly.) 

Heyn's  intercept  method  is  used,  the  average  grain  size  being 
determined  by  counting  the  number  of  grains  at  a  given  magnifi- 


FIG.   174. — Specimen. — After  hard  drawing. 

cation,  along  lines  of  known  length,  on  axes  perpendicular  to 
each  other  with  one  of  the  two  axes  parallel  to  the  direction  of 

30 


466  MICROSCOPIC  EXAMINATION  OF  METALS 

drawing  or  rolling.  If  the  material  is  apparently  composed  of 
very  non-uniform  crystals,  it  may  be  necessary  to  prepare  a  new 
surface,  and  take  a  third  crystal  count  along  a  line  at  right 
angles  to  the  other  two. 

Several  methods  of  expressing  the  numerical  values  of  the 
grain  size  are  in  use,  the  commonest  and  most  useful  system,  in 
the  case  of  equi-axed  grains,  is  to  indicate  the  number  of  grains 
per  unit  area  (square  inch  or  square  millimeter).  It  is  not  so 
satisfactory  to  report  the  average  area  of  a  grain,  although  this 
method  is  sometimes  used.  The  average  linear  dimensions  of 
the  grain  may  also  be  used  to  indicate  the  grain  size.  With 
elongated  crystal  grains,  the  grain  size  is  expressed  by  giving 
the  average  number  of  grains  per  linear  unit  in  two  (or  three) 
directions.  The  average  number  of  grains  per  unit  area  may  be 
given  as  well  as  the  ratio  of  length  to  width  of  the  grain. 

Of  the  various  methods  of  making  grain  size  measurements, 
the  most  convenient  one  is  that  of  Jeffries  referred  to  above. 
This  consists  in  projecting  the  magnified  image  of  the  specimen 
onto  a  ground  glass  plate  on  which  has  been  inscribed  a  circle 
79.8  mm.  in  diameter  (area  =  5,000  sq.  mm.).  The  ground 
glass  is  placed  in  position  in  the  metallographic  camera  with  its 
ground  surface  toward  the  specimen,  and  on  the  outer,  smooth 
surface  the  number  of  whole  crystals  included  in  the  circle  is 
counted.  This  may  be  done  conveniently  by  checking  each 
crystal  with  a  soft  (glass)  pencil.  The  number  of  grains  inter- 
secting the  circumference  is  then  counted,  and  0.5  of  this  number 
is  added  to  the  number  completely  included  in  the  circle,  giving 
a  close  approximation  to  the  whole  number  of  crystals  present. 
To  obtain  the  number  of  grains  per  square  millimeter,  the  crystal 
count  is  multiplied  by  a  factor  which  depends  on  the  magni- 
fication used.  These  factors  are  given  in  Table  XXX. 

Instead  of  using  a  circle,  as  indicated  in  Table  XXX,  it  is 
possible  to  use  a  rectangle  having  the  same  area  (5,000  sq.  mm.). 
The  following  dimensions  will  give  rectangles  of  approximately 
5,000  sq.  mm. : 

70.7  by  70.7  mm. 
65  by  77.0  mm. 
60  by  83.3  mm. 
55  by  91.0  mm. 


THE  ALLOYS  OF  COPPER 
TABLE  XXX 


467 


Magnification  used  (m) 

Diameter  of  circle 
in 
millimeters 

Multiplying  factor  (/) 
to  obtain  grains 
per  square  millimeter 

Full  size  

79.8 

0.0002 

10 

79.8 

0  0200 

25  

79.8 

0.1250 

50  
75 

79.8 
79  8 

0.5000 
1  1250 

100  

79.8 

2.0000 

150              

79.8 

4  5000 

200 

79  8 

8  0000 

250  

79.8 

12  5000 

300 

79  8 

18  0000 

500  

79.8 

50.0000 

750  
1000 

79.8 
79  8 

112.5000 
200  0000 

1500...  

79.8 

450  0000 

2000  

79.8 

800.0000 

NOTE — Brass  is  commonly  examined  at  a  magnification  of  75  diameters. 
If  the  diameter  of  the  inscribed  circle  is  increased  to  84.5  mm.,  or  a  rect- 
angle having  an  area  of  5,625  sq.  mm.  is  used,  the  multiplying  factor  "/" 
becomes  unity,  and  the  number  of  grains  in  the  larger  circle  is  the  same  as 
the  number  of  grains  per  square  millimeter. 


If  grain  size  measurements  are  made  on  a  rectangle,  instead 
of  with  a  circle,  the  method  is  practically  the  same  as  before. 
The  number  of  grains  in  the  inclosed  area  is  increased  by  half 
the  number  of  grains  intersecting  boundary  lines,  giving  a  close 
approximation  to  the  total  number  of  whole  grains  in  the  meas- 
ured area.  This  number  is  then  multiplied  by  the  suitable 
factor  from  Table  XXX  to  give  the  number  of  grains  per  square 
millimeter.  The  rectangle  may  be  inscribed  on  the  ground- 
glass  screen  of  the  camera,  or  the  measurements  may  be  made  on  a 
photomicrograph  of  known  magnification. 

Specifications  sometimes  require  the  grain  size  indicated  in 
terms  of  the  diameter  of  the  average  crystal  in  millimeters,  or 
the  area  of  the  average  grain  in  ju2.  The  following  formulas 
from  Jeffries'  paper  give  the  methods  of  calculation: 


468  MICROSCOPIC  EXAMINATION  OF  METALS 

z  =  completely  included  grains; 
w  =  boundary  grains; 
x  =  equivalent  number  of  whole  grains  in  5,000  sq.   mm. 

(circle  79.8  mm.  in  diameter  or  rectangle  with  an  area 

of  5,000  sq.  mm.) ; 
x  =  Y%  w  +  z. 
m  =  magnification; 
/  =  multiplying  factor  used  to  obtain  grains  per  sq.  mm.; 

(See  Table  XXX); 
/  -  m2/5,000; 

n  =  number  of  grains  per  square  millimeter;  n  =  fx. 
d  =  average  diameter  of  grain  in  millimeter;  d  =  l/\/n 
a  =  area  of  average  grain  in  /A     a  =  1,000,000/n 

All  that  has  been  said  with  regard  to  the  effects  of  work  on 
brass  applies  to  steel  as  well,  and  in  fact  the  theory  of  amorphous 
material  as  suggested  by  Beilby  and  developed  by  Rosenhain 
was  first  applied  to  mild  steel.  The  same  is  true  of  grain  growth 
and  grain  size  measurements  except  that  the  effects  of  slight 
temperature  changes  are  not  nearly  so  striking  with  steel  as 
with  the  non-ferrous  alloys  like  brass  and  bronze.  Grain  size 
measurement  is  seldom  required  in  the  specifications  of  worked 
steel,  but  grain  count  or  grain  size  is  a  frequent  requirement 
in  the  inspection  of  rolled  or  drawn  brass  in  the  form  of  sheet, 
tubes,  rods  and  the  like. 

0-brass. — The  striking  appearance,  due  to  the  twinning  of 
a-brass,  which  makes  the  measurement  of  grain  size  a  compara- 
tively easy  matter,  is  almost  wholly  lacking  in  the  class  of 
brasses  commonly  known  as  the  /3-brasses,  although  in  practice 
the  great  majority  of  them  are  mixtures  of  the  a  and  |8  crystals. 
The  best,  known  example  of  the  /3-brass  is  Muntz  metal,  an  alloy 
with  approximately  60  per  cent  Cu  and  40  per  cent  Zn.  It  has 
had  an  extended  use  in  the  industries,  largely  because  it  has  many 
good  qualities  and  is  relatively  cheap,  but  because  of  the  readiness 
with  which  it  undergoes  local  pitting  and  corrosion  its  use  is 
gradually  decreasing.  One  of  the  important  uses  of  the  metal 
has  been  in  the  production  of  condenser  tubes  and,  in  spite  'of 
its  certain  disadvantages,  its  use  has  by  no  means  been  discon- 
tinued. Figures  175  and  176  show  the  character  of  the  0-mixture 


THE  ALLOYS  OF  COPPER 


469 


FIG.  175. — Twins  of  a-brass  in  a  /3-field. 
75  X. 


as  it  is  found  in  condenser  tubes  differing  somewhat  in  compo- 
sition. The  tubes  were  subjected  to  a  considerable  amount  of 
cold  work  in  the  process  of 
drawing,  so  that,  as  is  to  be 
expected,  the  annealed  tube 
shows  the  characteristic 
twinned  structure  of  the 
a-brass  crystals  as  they  ap- 
pear in  the  /3-field.  Under 
the  action  of  alkaline  hydro- 
gen peroxide  the  a-brass  takes 
on  its  usual  brownish  tint, 
while  the  /3-crystals  are  prac- 
tically unaffected  or  slightly 
yellow.  The  microscope 
shows,  then,  the  manner  of 
distribution  of  the  two  crystal 
forms,  and  gives  to  the  metallographer  an  indication  of  the 
character  and  amount  of  heat  treatment  to  which  the  tube  has 
been  subjected  after  its  welding  or  drawing  has  been  finished. 
/3-brass  is  without  definite  crystal  form,  and  doesjiot  twin  under 
ordinary  conditions,  if  at  all. 

Since  Muntz  metal  consists 
of  two  crystal  forms,  it  is 
much  more  apt  to  segregate 
than  ordinary  a-brass,  and 
here  again  the  microscope  can 
be  of  great  service  to  the 
metal  tester.  A  few  illus- 
trations taken  from  technical 
practice  will  illustrate  the 
application  of  the  microscope 
to  defective  material  of  this 
sort.  Figure  177  shows  the 
distinct  layer  formation  in  a 

FIG.   l76.-/5-brass  in  field  of  twinned       condenser   tube    with    a-braSS 

w- Grass.      /oX- 

above  and  irregular  masses  of 

yellow  0-brass  distributed  through  the  a-field  in  the  lower  part  of 
the  photograph.     This  tube  was  etched  with  alkaline  peroxide  so 


470 


MICROSCOPIC  EXAMINATION  OF  METALS 


that  the  twinning  of  the  a-crystals  is  plainly  visible.  Figure  178 
illustrates  another  case  of  defective  material  in  which  the  a-brass 
is  irregularly  distributed  through  the  /3-field.  A  is  a  specimen 
etched  with  ammoniacal  ammonium  persulfate,  in  which  the 
island  of  light  colored  a-brass  is  distinctly  visible  in  the  field  of 
0-brass,  which  has  been  colored  almost  black  by  the  etching 
reagent.  B  is  a  part  of  the  same  tube,  but  etched  with  alkaline 
peroxide  so  that  the  brownish  colored  a  is  clearly  marked  in  the 
field  of  yellow  #. 


FIG.  177. — Layer  formation  in  defective  condenser  tube  showing  a-  and  a  + 

/3-layers.     75  X- 

The  appearance  and  physical  properties  of  0-brass  vary  over  a 
great  range,  depending  on  the  temperature  to  which  the  material 
is  heated  and  on  the  way  in  which  it  is  cooled  after  annealing. 
The  following  micrographs  of  Fig.  179  show  some  of  the  many, 
forms  in  which  /3-brass  occurs  following  variations  in  heat  treat- 
ment. The  chemical  composition  is  the  same  in  all  four 
specimens. 

Season  Cracking. — Copper,  brass,  and  bronze,  when  over- 
strained and  not  sufficiently  annealed,  are  subject  to  a  remark- 
able and  dangerous  action  known  as  season  cracking.  If  the 


THE  ALLOYS  OF  COPPER 


471 


shell  case,  tube  or  other  article,  which  has  been  subjected  to 
severe  cold  work  without  the  relief  of  annealing,  is  allowed  to 


A.    Etched   with    NH4OH   and    (NH4)2S2O8.     a-brass   very   slightly   attacked. 

75  X. 


B.  Part  of  the  same  tube  etched  with  NH4OH  and  H2O2.     75  X- 
FIG.  178. — Formation  of  islands  of  a-brass  in  /3-field. 

stand  for  some  length  of  time,  especially  if  the  material  is  stored 
in  a  moist  atmosphere  or  near  salt  water,  a  spontaneous  decompo- 


472 


MICROSCOPIC  EXAMINATION  OF  METALS 


sition  of  the  material  takes  place,  leading  to  the  formation  of  small 
or  large  "  season  cracks."  Failure  of  brass  and  bronze  parts  from 
this  cause  has  lead  to  serious  damage  and  financial  loss,  so  seri- 
ous that  the  subject  was  investigated  by  the  Bureau  of  Standards1 


C  D 

FIG.    179. — Muntz    metal    showing    variations    with    heat    treatment.      100  X- 

(Homerberg.) 

in  connection  with  breaks  in  the  Catskill  Aqueduct,  the  Minne- 
apolis Filtration  Plant  and  some  manganese  bronze  bolts  used  in 
the  Panama  Canal  lock  gates. 

1  Bureau  of  Standards  Technical  Paper  No.  82,  January,  1917. 


THE  ALLOYS  OF  COPPER 


473 


While  the  detection  of  this  difficulty  is  really  a  chemical 
rather  than  a  metallographic  problem,  the  question  is  one  com- 
monly left  to  the  metallographer  for  solution.  While  the  exact 
reagent  to  use  and  the  method  of  applying  the  test  is  still  a 
subject  of  discussion  and  much  experimental  work,  the  method  as 
recommended  by  the  Ordnance  Department  may  be  taken  as 
representing  the  general  nature  of  the  test.  The  suspected 
material  is  immersed  in  an  excess  of  a  solution  of  1.5  per  cent 
mercuric  chloride  or  mercuric  nitrate,  and  if  the  overstrain  has 
been  severe  the  effects  of  " season  cracking"  are  so  greatly 
accelerated  that  cracks  often  leading  to  complete  break  down  of 
the  material  may  be  started  at  once.  It  is  generally  accepted 
that  if  the  material  will  stand  immersion  in  the  mercuric  salt  for 
a  period  of  4  hr.,  it  may  be  considered  free  from  those  strains 
which  would  lead  to  season  cracking,  either  during  the  interval 
of  storing  or  during  long  continued  use.  The  action  of  the 
mercury  salt  seems  to  be  due  to  the  deposition  of  metallic  mercury 
and  its  diffusion  into  the  metal  at  those  places  in  which  the 
amount  of  amorphous  material  is  greatest. 

Other  Copper  Alloys. — In 
addition  to  the  common 
brasses  and  bronzes  with 
which  the  metal  tester  usually 
has  to  deal,  there  are  many 
more  complex  alloys  whose 
mechanical  characteristics,  as 
far  as  their  microscopic  ex- 
amination is  concerned,  are 
much  the  same  as  those  of 
trie  commoner  metals.  Ad- 
miralty metal,  for  instance, 
is  ordinary  70—30  brass  in 
which  from  1  to  1.5  per  cent 
of  the  zinc  is  replaced  by  tin, 
making  the  alloy  somewhat 

less  readily  corroded,  and  in  naval  brass  the  same  substitution  of 
tin  is  made  in  an  alloy  of  the  Muntz  metal  type  for  the  same  reason. 
In  both  cases  the  appearance  of  the  resulting  alloys  is  substan- 
tially the  same  as  that  of  the  corresponding  common  brasses,  and 


FIG. 


180. — Aluminium    bronze. 
75  X. 


474  MICROSCOPIC  EXAMINATION  OF  METALS 

the  effects  of  cold  work  and  annealing  are  indicated  in  the  same 
way  as  with  the  simpler  alloys.  Aluminium  bronze,  made  by  alloy- 
ing copper  with  an  amount  of  aluminium  not  exceeding  1 1  per  cent, 
is  sometimes  submitted  for  examination.  It  is  seldom  used, 
except  in  the  cast  form,  where  it  is  characterized  by  the  very 
irregular  distribution  of  the  dendritic  crystals,  which  probably 
accounts  for  the  high  tensile  strength  and  ductility  of  this  mater- 
ial. Figure  180  shows  the  closely  interlocked  structure  of  cast 
aluminium  bronze  as  compared  with  the  much  more  open  struc- 
ture of  phosphor  bronze,  shown  on  p.  457,  Fig.  164. 

Tin-antimony  Alloys,  Babbitt  Metal    and  Other  White  Bear- 
ing Alloys. — The  "white"  alloys  used  for  light  bearings  commonly 


FIG.  181. — Antimony  in  a  lead-antimony  eutcctio  matrix.     75  X-     (Homerberg.) 

contain  tin,  antimony  and  lead  in  varying  amounts,  often  as  in 
the  case  of  Babbitt  metal  with  the  addition  of  copper.  The  char- 
acteristic feature  of  the  group  is  the  existence  of  the  hard,  cubical 
crystals  of  the  compound  SbSn  which,  in  the  case  of  Babbitt 
itself,  is  probably  the  material  which  gives  to  the  alloy  its 
valuable  properties.  In  the  simple  lead-antimony  alloys,  less 
frequently  used  in  practice,  the  hard  material  is  composed  of  anti- 
mony crystals  imbedded  in  the  lead  matrix.  In  either  case  the 
microscope  is  of  great  value  in  determining  the  regularity  or 
irregularity  of  distribution  of  the  hard  grains  in  the  soft  matrix. 
Figure  181  shows  the  irregular  shape  and  uneven  distribution  of 


THE  ALLOYS  OF  COPPER 


475 


antimony  crystals  in  the  lead  base  of  a  badly-cooled,  white  bear- 
ing.    In  the  case  of  the  tin-antimony  alloys,  there  is  a  marked 


B 

FIG.   182. — Variations  in  size  and  distribution  of  SbSn  in  white  metal. 

tendency  for  the  SbSn  crystals  not  only  to  vary  enormously  in 
size  but  also  to  segregate  during  the  cooling  of  the  melted  alloy, 


476  MICROSCOPIC  EXAMINATION  OF  METALS 

with  results  which  are  quite  unsatisfactory,  and  yet  are  exceed- 
ingly difficult  to  detect  by  means  other  than  microscope  control. 
Figure  182A  shows  abnormally  large  crystals,  while  B  in  another 
part  of  the  same  casting  shows  not  only  comparatively  small  masses 
of  the  SbSn  compound  but  also  a  most  unequal  distribution  of 
the  bearing  material  in  the  matrix.  These  photographs  illustrate 
another  characteristic  of  Babbitt  metals  which  requires  careful 
microscopic  control,  namely  the  influence  of  the  cooling  rate  on 
the  crystal  size.  The  usual  method  of  lining  a  bronze  bushing 
with  Babbitt  metal  is  to  pour  the  molten  Babbitt  in  the  cylindri- 
cal opening,  left  between  the  inner  wall  of  the  bushing  to  be 
lined  and  the  outside  of  an  iron  or  steel  core.  The  factors  which 
influence  the  distribution  of  the  crystalline  compounds  in  the 
lining  are  essentially  the  temperature  of  the  iron  core  and  the 
temperature  of  the  bronze  bushing.  The  latter  temperature 
cannot  be  changed  to  any  great  extent,  but  the  temperature  of  the 
core  can,  and  should,  be  carefully  regulated  for  the  most  success- 
ful results.  The  two  crystals  which  separate  from  common 
Babbit  are  CusSn  and  SbSn.  The  size  and  character  of  each  is 
largely  determined  by  the  temperature  of  the  core  against 
which  the  melted  metal  is  poured.  The  effects  of  changing  the 
cooling  rate  by  changing  the  temperature  of  the  mold  are  illus- 
trated in  the  photomicrographs  of  Fig.  183.  The  alloy  was  the 
same  in  each  case,  and  the  temperature  from  which  the  metal  was 
poured  was  carefully  controlled,  so  that  the  only  varying  factor- 
was  the  temperature  of  the  oil-bath  in  which  the  receiving-tube 
was  immersed.  It  is  very  evident  that  a  marked  difference  in 
crystal  size  is  produced  by  these  temperature  changes,  and  by 
determining  the  most  favorable  size  for  a  given  purpose  it  is  possi- 
ble to  control  the  physical  properties  chiefly  the  frictional  resis- 
tance of  the  material,  within  narrow  limits.  Metallographic 
control  of  Babbitt-lined  bearings,  both  with  regard  to  the  crystal 
size  and  with  regard  to  the  evenness  of  distribution  of  the  crystal- 
line material,  has  been  adopted  as  part  of  the  testing  routine  of 
several  large  industrial  plants  engaged  in  making  bearings. 
It  is  hardly  necessary  to  suggest  that  in  sampling  a  material  in 
which  segregation  occurs  so  commonly,  and  in  which  the  size  of 
the  crystal  masses  may  vary  so  widely,  the  microscope  can  be  of 
great  service  to  the  chemist  in  the  selection  of  a  sample  of  suitable 


THE  ALLOYS  OF  COPPER 


477 


size,  from  the  right  location  in  the  specimen  to  be  tested,  so  that 
the  analysis  may  truly  represent  the  composition  of  the  metal. 
Finally,  the  danger  of  overestimating  the  value  of  the  micro- 
scope must  be  emphasized.     The  microscope  is  a  valuable,  and 


C  D 

FIG.  183. — Babbitt  metal  showing  effect  of  cooling  rate  on  crystal  size.     75  X. 

(Federhen.) 

in  some  cases  an  indispensable,  tool  for  the  metal  tester,  but  the 
inexperienced  metallographer  must  realize  fully  that  the  correct 
interpretation  of  microscopic  appearances  in  doubtful  cases  needs 
much  practice  and  experience  with  metals  under  widely-differing 


478  MICROSCOPIC  EXAMINATION  OF  METALS 

conditions  of  composition,  heat  and  mechanical  treatment.  The 
microscope  should  always  be  considered  as  but  one  of  the  means 
available  for  the  inspection  of  metals  and  alloys.  It  is  most 
certainly  true  that  the  value  of  proper  sampling  in  technical 
work  has  not  been  properly  recognized  or  appreciated,  and  it  is 
evident  that  the  microscope  can  be  of  great  value  in  many  cases 
in  getting  samples  which  are  really  representative. 

Quite  often,  in  practice,  the  chemist  in  charge  of  an  analytical 
laboratory,  who  is  responsible  for  the  accuracy  of  the  results,  has 
nothing  whatever  to  say  about  the  way  in  which  the  samples 
submitted  to  him  for  analysis  shall  be  taken.  He  can  assume  the 
responsibility  for  correct  chemical  analyses,  but  cannot  guarantee 
that  the  values  given  for  different  constituents  actually  represent 
the  average  composition  of  the  material,  since,  as  has  been  shown, 
the  composition  of  the  sample  is  not  necessarily  uniform  through- 
out its  entire  cross-section,  but  is  often  quite  the  reverse. 

For  this  reason,  judgment  based  on  chemical  analysis  alone  is 
not  always  correct  as  the  analytical  results  are  influenced  to  a 
marked  degree  by  the  methods  of  sampling.  Control  analyses, 
made  by  different  chemists  on  borings  from  the  same  piece,  are 
of  value  only  when  the  sample  to  be  analyzed  has  been  shown  by 
the  microscope  to  be  homogeneous,  or  at  least  uniform  through- 
out its  whole  cross-section.  Much  of  the  disagreement  among 
chemists  has  no  doubt  been  due  to  incorrect  sampling  with  the 
resulting  lack  of  uniformity  in  the  samples  analyzed.  It  has 
been  remarked1  that  "The  one  great  argument  against  the  use 
of  chemistry  for  the  grading  of  iron  has  been  that  the  work  of  the 
chemists  varied  so  much  that  it  was  impossible  to  obtain  any- 
thing like  uniform  results."  That  the  chemist  has  been  responsi- 
ble for  these  conditions  to  a  very  limited  extent  has  been  shown. 
Irregularities  in  the  chemical  composition  of  the  sample,  due  to 
local  segregation,  are  often  far  greater  than  the  possible  errors  of 
analysis.  This  is  true  not  only  of  pig  iron  but  also  of  all  other 
kinds  of  iron  and  steel  and,  to  a  less  degree,  of  the  brasses,  bronzes 
and  other  non-ferrous  alloys.  Metallography  is  of  great  value 
to  the  chemist  in  helping  him  to  detect  these  local  differences,  and 
indeed  it  is  impossible  to  determine  such  differences  in  many 
cases  except  by  the  microscope. 

1  H.  E.  FIELD,  Iron  Trade  Review,  February,  1903. 


THE  ALLOYS  OF  COPPER  479 

The  cost  of  installing  a  simple  metallographic  outfit  is  not 
excessive,  especially  if  an  old  microscope  is  made  over  for  the 
purpose  by  the  addition  of  a  prism  or  plate  illuminator.  It  seems 
very  desirable  for  the  protection  of  the  chemist  and  in  the  interest 
of  the  employer: 

1.  That  the  chief  chemist  should  be  trained  in  Metallography 
in  so  far  as  it  applies  to  the  inspection  and  sampling  of  common 
alloys. 

2.  That  a  metallographic  equipment,  even  though  it  is  a  very 
small  one  without  photographic  facilities,  should  be  connected 
with   every  laboratory   dealing   with   the   analysis   of   metallic 
substances. 

3.  That  in  all  cases  the  taking  of  samples  should  be  directly 
in  charge  of  the  one  responsible  for  the  subsequent  analysis.     The 
control  of  the  sampling  not  only  should  cover  the  places  on  the 
specimen  from  which  the  sample  is  to  be  taken  but  should  also 
determine  the  method  of  sampling,  whether  by  boring,  filing  or 
planing  and  the  way  in  which  the  samples  should  be  mixed  and 
handled,    after   they  reach   the   laboratory.     If   metallographic 
laboratories  are  already  established,  as  is  the  case  in  many  of  the 
larger  plants  in  the  metal  industry,  they  should  be  in  intimate 
touch  with  the  work  of  the  chemical  laboratory,  so  that  each 
department  may  be  of  service  to  the  other. 


INTERNATIONAL  ATOMIC  WEIGHTS,  1921 


Sym- 
bol. 

Atomic 
Weight. 

Sym- 
bol. 

Atomic 
Weight. 

Aluminum 

Al 

27  1 

Molybdenum 

Mo 

96  0 

Antimony  

Sb 

120.2 

Neodymium  .  .      .    . 

Nd 

144  3 

Argon  

A 

39.9 

Neon  .  . 

Ne 

20  2 

Arsenic 

As 

74  96 

Nickel 

Ni 

58  68 

Barium  

Ba 

137.37 

Niton    (radium   ema- 

Bismuth   

Bi 

208  0 

nation)  .... 

Nt 

222  4 

Boron 

B 

10  9 

Nitrogen 

N 

14  008 

Bromine  

Br 

79.92 

Osmium  

Os 

190  9 

Cadmium  .... 

Cd 

112.40 

Oxygen.  . 

o 

16  00 

Caesium 

Cs 

132  81 

Palladium 

Pd 

106  7 

Calcium  

Ca 

40.07 

Phosphorus  

P 

31.04 

Carbon 

c 

12  005 

Platinum.  . 

Pt 

195  2 

Cerium 

Ce 

140  25 

Potassium 

K 

39  10 

Chlorine  

Cl 

35.46 

Praseodymium  

Pr 

140.9 

Chromium  .  . 

Cr 

52  0 

Radium.  .  . 

Ra 

226.0 

Cobalt 

Co 

58  97 

Rhodium 

Rh 

102  9 

Columbium  

Cb 

93.1 

Rubidium  

Rb 

85.45 

Copper 

Cu 

63.57 

Ruthenium  

Ru 

101.7 

Dysprosium 

Dy 

162  5 

Samarium  . 

Sa 

150  4 

Erbium    

Er 

167.7 

Scandium  

So, 

45.1 

Europium  
Fluorine  

Eu 
F 

152.0 
19.0 

Selenium  
Silicon  

Se 
Si 

79.2 

28.3 

Gadolinum 

Gd 

157  3 

Silver 

Ag 

107  88 

Gallium 

Ga 

70  1 

Sodium 

Na 

23  00 

Germanium 

Ge 

72.5 

Strontium  

Sr 

87.63 

Glucinum  
Gold                 

Gl 
Au 

9.1 
197.2 

Sulphur  
Tantalum  

S 
Ta 

32.06 
181.5 

Helium 

He 

4.00 

Tellurium  

Te 

127.5 

Holmium  
Hvdrotren 

Ho 
H 

163.5 
1  008 

Terbium  
Thallium 

Tb 
Tl 

159.2 
204  0 

Indium 

In 

114.8 

Thorium  

Th 

232.15 

Iodine 

I 

126.92 

Thulium  

Tm 

168.5 

Iridium  

Ir 

193.1 

Tin  

Sn 

118.7 

Iron 

Fe 

55  84 

Titanium                    .  . 

Ti 

48.1 

Kr 

82  92 

Tungsten 

W 

184.0 

Lanthanum 

La 

139.0 

Uranium  

u 

238.2 

Lead 

Pb 

207  20 

Vanadium  

V 

51.0 

Lithium  
Lutecium 

Li 
Lu 

6.94 
175.0 

Xenon  
Ytterbium  (Neoyt  ter- 

Xe 

130.2 

IMagnesium 

Me 

24.32 

bium)  

Yb 

173.5 

IVlanganese 

Mn 

54.93 

Yttrium  

Yt 

89.33 

IMercury 

He 

200.6 

Zinc  

Zn 

65.37 

Zirconium  

Zr 

90.6 

INDEX 


Abnormal  formations  on  gray  cast 

iron,  420 

Abrasive  for  polishing  metals,  338 
powders,  341 
suspensions,  341 
Absorption  tubes  for  carbon  dioxide, 

13,  20,  25,  33 
Acetic  acid,  curve  in  electrometric 

titration,  274 
Acid    ammonium    sulfate    solution, 

105 

nitrate  solution,  112 
sulfite  solution,  92 
etching  with,  342 
standardization  of,  14 
Admiralty  metal,  473 
Air  bath  for  heating  crucibles,  83 

dehydrating  silicic  acid,  118 
Alcoholic  hydrochloric  acid  solution 

for  etching,  358 
nitric  acid  solution  for  etching, 

358 
Alkali,  etching  with,  342 

standard  solution  of,  14 
Alkalimetric  method  for  determining 

phosphorus  in  steel,   94 
Alkaline     hydrogen     peroxide     for 

etching,  449 

Allen,  A.  H.,  nitrogen  in  steel,  243 
Alloy  steels,  determination  of  phos- 
phorus in,  109 
Allotropic  forms  of  iron,  354 
Alloys,  non-ferrous,  307 

of  copper,  microscopic  examina- 
tion, 450 

Alumina,  levigated,  339 
Aluminium  bronze,  474 

31  481 


Aluminum     bronze,      analysis     of, 

310 
determination  after  the  silicon 

determination,  119 
in  ignited  silica,  220 
iron  and  steel,  220 
non-ferrous  alloys,  310 
presence  of  zirconium,  259, 

260 
phosphate,     determination     of 

chromium  in,  222 
test  analyses  in  steel,  223 
Alundum  F,  341 

sand,  300 

Amalgamated  zinc,  106 
Ammonia,    oxidation    by    bromine, 

79 

solution  for  phosphorus  deter- 
mination, 92 
Ammoniacal  cadmium  solution,  134, 

136 

Ammonium  acid  sulfate  solution  for 
vanadium  determination, 
209 

bisulfite  solution,  92,  105 
chloride  solution  as  a  standard, 

244 
molybdate    solution,    93,     100, 

209,  315 

nitrate  solution,  112 
persulfate  for  etching  brass  and 

bronze,  449 

phosphate    solution    for    vana- 
dium determination,  209 
thiocyanate    for    cobalt    deter- 
mination, 227 
Amorphous  cementing  material,  459, 

468 
Ampere,  definition,  265 


482 


INDEX 


Amyl  alcohol  and  ether  mixture  for 
nickel-cobalt      separation, 
227 
Andrews,      cyanide      method      for 

determining  nickel,  182 
Annealed  malleable  iron,  406 
Annealing  brass  and  bronze,  460 
cause  of  superficial  decarboniza- 

tion,  397 
effect  on  gray  iron,  419 

white  iron,  404 
for    the    sulfur    determination, 

135 

steel,  390 
the  sample,  425 
unintentional,  409 
Antimonous  antimonate,  309 
Antimony,  311 

behavior  toward  nitric  acid,  309 
determination  in  bearing  metals, 

313,  314 
by    permanganate    titration, 

316 

lead  eutectic,  474 
tetroxide,  309 
tin  alloys,  474 

compound  in  alloys,  475 
Apparatus  for  carbon  determination, 
11,    20,    21,    24,    32,    37, 
300 
distilling  arsenic  tribromide,  225 

bromine,  215 

electrolytic  depositions,  145, 179 
electrometric  titrations,  276 
filtering  barium  carbonate,    18 
Gooch  crucibles,  81 
nitrogen  in  iron  and  steel,  245 
oxygen  in  iron  and  steel,  249, 

253,  254 

reducing  titanium  solutions,  237 
with  amalgamated  zinc,  105 
shaking  with  ether,  71 
Volhard       determination       of 

manganese,  61 
Archbutt,  determination  of  sulfur  in 

the  presence  of  iron,   129 
Arsem  vacuum  furnace,  252 


Arsenic,    determination    in    copper 
alloys,  318 
iron  and  steel,  224 
effect  on  properties  of  copper, 

318 

determination      of      phos- 
phorus, 110 

iodometric  titration  of,  318 
reduction  by  cuprous  chloride, 

224 
removal     by     treatment     with 

hydrobromic  acid,  111 
separation  from    molybdenum, 

192 
Arsenite     solution    for     manganese 

determination,  51 

Arthur,  cyanide  method  for  deter- 
mining nickel,  182 
Asbestos  filter,  preparation  of,  34,  57 
for  Gooch  crucibles,  80 
ignited,  34,  45 
Ascarite,  20 

Atomic  weight  table,  480 
Austenite,  7,  357,  359,  390 
Autogenous  welds,  x-ray  study  of, 

443 
Axle  bearing,  case  hardened,  396 


Babbitt  metal,  474,  476,  477 
Bailey,   C.   H.,  hydrogen  electrode, 

291 

Bailey's  Gooch  crucible  holder,  81 
Baker,  J.  C.  and  Van  Slyke,  L.  L., 

electrometric        titrations, 

291 
Bamber    method    for    determining 

sulfur  in  steel,  131 
Bancroft,    W.    D.,    oxidation    cells, 

291 

Barba,     W.     P.,    determination    of 
chromium  in  steel,  152 

phosphorus  in  steel,  104 
Barium   carbonate   suspension,    150 
hydroxide  method  for  determin- 
ing carbon,  11,  18 


INDEX 


483 


Barium  hydroxide  solution,  electric 
resistivity  of,   296,   297, 
298 
for  carbon  determination, 

9,  14 
sulfate,  danger  of  overheating, 

139 

occlusion  by,  129 
precipitation  in  presence  of 

iron,  128,  129 
Barneby  and  Isham,  determination 

of  titanium,  231 
Barton,     L.     E.,    determination    of 

nitrogen  in  steel,  246 
Basic  acetate  method  for  separating 
iron  and  manganese,  78, 
83 

for  phosphorus  determina- 
tion, 97,  101 
bessemer-bar,    segregation    in, 

385 

ingot,  etched,  375 
Bauer,  O..  annealing  with  charcoal, 

426 

Baumann's  test  for  sulfide,  378 
Bearing  metals,  474 

chemical  analysis  of,  312 
microscopic   examination  of, 

446 
rapid     volumetric     analysis, 

315 
Behrend,  R.,  electrometric  analysis, 

291 
Beilby,  amorphous  cement  theory, 

459,  468 
Belcher,   D.,  volatility  of  tungsten 

trioxide,  196 

Berzelius,  sulfur  determination  by 
weighing  silver  chloride, 
128 

Bismuth-tin  eutectic  alloy,  350 
Bismuthate  method  for  determining 

chromium,  154,  283 
manganese,  49,  53,  54 
Bjerrum,  N.,  electrometric  analysis, 

291 
Black  heart,  405 


Blair,  A.  A.,  basic  acetate  method 
for  determining  phosphorus, 
101 
determination  of  vanadium  in 

steel,  210 
ether   method  for  determining 

molybdenum,  192 
permanganate  method  for  deter- 
mining phosphorus,  101 
Blank  arsenic  determination,  318 
carbon  determination,  22,  26,  35 
on  the  Jones'  reductor,  106 
silicon  determination,  120 
sulfur  determination,  139 
Blow  holes  shown  by  x-ray  examina- 
tion, 444 

Boiler  plate,  red  short,  388 
sampling  of,  432 
segregation  in,  388 
wedge  formation  in,  431 
Bovie,    W.    T.,    potentiometer    for 

electrometric  work,  291 
Brass,  307 

alpha  and  beta,  454,  456,  468, 

469 

analysis  of,  319 
annealing,  460 
cold  worked,  463 
"dead  soft,"  462 
'  equilibrium  diagram,  452 
microscopic  examination  of,  446 
polishing  and  etching,  448 
season  cracking  of,  470 
shell  case,  photomicrograph  of, 

447 

sieves,  437 
slag  areas  in,  457 
strained,  461 
worked,  458,  463 

Brearly,  cyanide  method  for  deter- 
mining nickel,  182 
Bromine,     action     on     manganese, 
ammonia  and   ammonium 
salt,  79 
.Bronze,  307 

analysis  of,  319 
annealing,  460 


484 


INDEX 


Bronze,    equilibrium  diagram,  453, 

456 

decorative  castings,  456 
lead  drops  in,  451 
microscopic  examination  of,  446 
polishing  and  etching,  448 
season  cracking,  470 
worked,  458 

Brunck,  precipitation  of  nickel,  175 
Bunker,    J.    W.    M.,   hydrogen   ion 

concentration,  291 
Bunsen    apparatus    for    vanadium 

determination,    215 
valve,  237 

Burgess,  G.  K.  and  LeChatelier,  H., 
high  temperature  measure- 
ment, 425 
Burned  copper  alloys,  456 

steel,  391 

Burrows,  C.  W.,  441,  442 
Bushelled  wrought  iron,  367 


Cadmium-ammonia    chloride    solu- 
tion, 134,  136 

Cain,    J.    R.   and   Maxwell,  L.   C., 
apparatus    for    electrometric 

work,  300 
determination    of    carbon    in 

steel,  11,  295 
Witmer,   L.    F.,  determination 

of  vanadium,  210 
Calibration  of  a  flask  with  a  pipette, 

84 

Calomel  cell  or  electrode,  272,  278 
Camera        for      photomicrographic 

work,  342 

Campagne,  E.,  precipitation  of  am- 
monium metavanadate,  217 
reduction  of  vanadic  acid,  211 
Campbell,     cyanide      method     for 

determining  nickel,    182 
Carbide  of  iron,  7 
Carbon,  apparatus  for  determining, 

11,  20,  21,  24,  32,  37 
as  carbide,  graphite  and  temper 
carbon,  7 


Carbon,  colorimetric  determination 

in  steel,  46 
content  of  cast  iron  changed  by 

remelting,  403,  418 
spiegel  iron,  404 
determination        by       barium 
hydroxide  methods,  11,  18 
Cain  method,  11 
Corleis   chrome-sulfuric   acid 

method,  23 
Deiss  method,  37 
direct  combustion,  11,  19,  37 
potassium-cupric         chloride 

method,  32 

wet  combustion  method,  23 
dioxide,  absorption  by  ascarite, 

21 

barium  hydroxide,   9,    13 
potassium  hydroxide,  9,  33 
soda  lime,  9,  25 
electrometric  determination,  295 
in  gray  cast  iron  powder,  438 
results,  36 
segregation,  383 

basic-bessemer    steel,    376 
in  a  connecting  rod,  384 
in  a  malleable  casting,  408 
total,  8 
Carpenter  and   Elam,   non-metallic 

inclusions,  458 
Cartridge    brass,    cold-worked    and 

strained,  345,  463 
Case-hardened  specimens,  396 
Cast  iron,  analysis  of,  411 
annealed,  406 
chilled,  399 
crystals  in,  402 
determination  of  phosphorus 

in,  96 

manganese  in,  53 
silicon  in,  120,  122 
disintegration  of,  421 
effect  of  annealing  and  remelt- 
ing, 403,  418 
gray,  410,  412,  439 
inequalities  in   the  chemical 
composition,  439 


INDEX 


485 


Cast  iron,  sampling  of,  399,  435,  436 

white,  399 
steel,    microscopic  examination 

of,  369,  370 
Catalyzer  for  carbon  combustions, 

12 

Caustic  potash  solution  for  absorp- 
tion of  carbon  dioxide,   9 
Cavities  in  iron  and  spiegel,  crystals 

in,  402 
Cell,  calomel,  278 

concentration,  270,  273 
Daniell,  267,  269,  270 
electrolytic,  267,  269,  270 
Cementing  material,  amorphous,  459 
Cementite,  7,  358,  363,  399,  404 

etched  by  Kourbatoff's  reagent, 

358,  363 

spheroidized,  362 
Cerium,  effect  on  determination  of 

zirconium,  262 

Chamois  leather  for  polishing  speci- 
mens, 340 

Chemical  composition,  affected  by 
remelting  cast  iron,  403, 418 
inequalities  in,  439 
Chilled  castings,  characteristics  of, 

399 

Chrome-sulfuric  acid  for  determin- 
ing carbon  in  steel,  26 
method,  23 

Chromic  oxide,  purification  of,  163 
Chromium,  colorimetric  determina- 
tion, 151 
determination  after  the  silicon 

determination,  119 
sulfur    determination,    140 
in    ignited    aluminum    phos- 
phate, 222 

by  Barba's  method,  152 
barium     carbonate 

method,  150 
bismuthate  method,  154, 

283 

.  ether  method,  155 
chlorate  method,  153 
fusion  method,  165 


Chromium,    effect    on    manganese 

determination,  54,  69 
electrometric        determination, 

280,  283 

indirect  titration  with  perman- 
ganate, 153 
thiosulfate,  161 
in  insoluble  material,  167 
iodometric   determination,    161 
occurrence  in  iron  and  steel,  150 
precipitation      as      mercurous 

chromate,  162 
separation    from    iron    by    the 

ether  method,  155 
magnesium-sodium  carbon- 
ate, 152,  167 
sodium  peroxide,    160 
phosphorus,    vanadium    and 

tungsten,  163 
Cinchonine  hydrochloride  solution, 

196 

method  for  determining  tung- 
sten, 195 
Clark,  W.  M.,  electrometric  analysis, 

291 

Clarke,  F.  W.,  separation  of  anti- 
mony and  tin,  311 
Cleaning  electrodes,  327 

test  pieces  for   metallographic 

study,  424 
Clevenger,     C.     B.,    hydrogen    ion 

concentration,  292 
Cobalt,  227 

separation    from    nickel,     176, 

227 

Cold-worked  steel,  392,  393 
Colloidal  silicic  acid,  115 
Colloids,  sol  and  gel  states,  115 
Color    screens    for    metallographic 

work,  344 

Colorimeter  for  titanium  determina- 
tion, 235 

Colorimetric  method  for  determin- 
ing carbon,  46 
copper,  145 
manganese,  70 
sulfur,  129 


486 


INDEX 


Colorimetric  method  for  determin- 
ing titanium,  234 
Colors  of  steel  at  high  temperatures, 

425 

Combustion  boats,  13,  41 
catalyzers,  12 
train,  12,  21,  24,  33,  40 
tubes,  12,  33,  40 
Comstock,   non-metallic   inclusions, 

458 

Concentration  cells,  270,  273 
Condenser  tubes,  defective,  470 

of  Muntz  metal,  468,  469 
Connecting  rod,  defective  owing  to 

inclusions,  384 
screws,   segregation  in,   383 
Contat-Gockel  valve,  237 
Cooling    curves    of    lead  and  lead- 
antimony  alloys,  347,  348 
effect  of  rate  upon  separation  of 

graphite  in  iron,  410 
Copper  alloys,  microscopic  examina- 
tion of,  446,  450,  473 
ammonium     chloride     etching 

with,  380 

colorimetric  determination,  145 
determination     after     determi- 
nation of  silicon,  119 
sulfur,  140 
removal  of  iron,  144 
as  oxide,  143 
by    iodometric   method,   146, 

317,  328 

in  bearing  metal,  313 
electrolytic     determination     in 

brass  and  bronze,  323 
iron  and  steel,  145 
-nickel  equilibrium  diagram,  354 
nitrate  solution  as  standard,  144 
occurrence  in  iron  and  steel,  142 
oxide  eutectic  in  copper,  457 
-potassium  chloride,  use  of,  9 
precipitation  as  sulfide  iron  acid 

solution,  142 
reaction  with  nitric  acid,  308 

sulfuric  acid,  307 
-silver  equilibrium  diagram,  352 


Copper  alloys,   solid    solution  with 

zinc,  454 

spongy  deposits  of,  325 
sulfate  solution,  144 
sulfide  ignition  to  oxide,  143 

oxidation  of,  142 
Copper-tin  compound  in  alloys,  476 

equilibrium  diagram,  453 
-zinc  equilibrium  diagram,  452 
Corleis  flask  and  method  for  deter- 
mining carbon,  23 
Coulomb,  electrical  unit,  264,  265 
Cracking,  season,  470 
Cramer       contrast       photographic 

plates,  343 

Cream  of  tartar,  fusion  with,  164 
Crotagno,  oxidation  potentials,  292 
Crystal  distortion  in  brass,  345 

grains  in  steel,  significance  of, 

393 
in  cavities  of  iron  and  spiegel, 

402 

twinning,  461,  464 
Cumming,    A.    C.   and   Abegg,   R., 

liquid  potentials,  292 
Cupferron,  use  in  determination  of 

zirconium,  261 
Cupric-ammonium       chloride       for 

etching  steel,  373 
potassium  chloride  for  carbon 

determination,  9 
Cuprous      chloride      for      reducing 

arsenic  acid,  224 
iodide,  328 
thiocyanate,  317 
Cyko  paper  for  sulfur  prints,  378 


D 


Daniell  cell,  267,  269,  270 
Davey,  x-ray  photograph,  444,  445 
"Dead  soft"  brass,  462 
Decarbonizing  steel,  396 
Decomposed  cast  iron,  422 
Decomposition  potential,  268 
Decorative  bronze  castings,  456. 
Dehydration  of  silicic  acid,  116,  119 


INDEX 


487 


Deiss,  E.,  determination  of  carbon 

in  steel,  37 
tungsten  in  steel,  197 
Dendritic   structure  of  phosphorus 

bronze,  457 

Desch,  metallography,  338 
Desha  and  Acree,  use  of  hydrogen 

electrode,  292 
Desiccator,  cooling  in,  82 
Diacetyldioxime,  175 
Diamond  mortar,  426 
Dimethyl  glyoxime,  recovery  from 

nickel  precipitates,  178 
solution       for      determining 

nickel,  176 

Disintegration  of  cast  iron,  422 
Distilled  water  free  from  ammonia, 

244 

Distribution  coefficient  and  law,  71 
Divanadyl  salt,  206 
Double     chloride     of    copper    and 
ammonium,  373 

potassium,  9,  32 
Drown,    T.    M.,    determination    of 

phosphorus    in    steel,    104 

silicon  in  iron  and  steel,  119 

Dudley,    C.    B.,    determination    of 

phosphorus    in    steel,    104 
Duolistic  nomenclature,  188 
Dutoit    and    Duboux,   titration   of 

organic  acids,  292 


E 


Electric  furnace  for  carbon  combus- 
tions, 11,  37 

oxygen  determination,  300 
temperature  obtained  with,  42 
motor  and  stirrer,  279 
Electrical  resistivity,  264 

of    barium    hydroxide    solu- 
tions, 296-7 
Electricity,  intensity  and  capacity 

factors  of,  264 
Electro-chemical  series,  267 
Electrodes,  cleaning,  327 
gauze,  145,  323 


Electrodes,  platinum  crucible  plate 

and  spiral,  323 
rotating,  323 
Electrolytic  apparatus  of  Frary,  145, 

179 

determination  of  cobalt,  227 
copper,  145,  323,  326 
lead,  323,  326 
nickel,  178 
zinc,  332 

solution  pressure,  266 
Electrometric  methods,  advantages 

of,  282 

apparatus,  276 
applicable  to  steel  analysis, 

264 

bibliography,  291 
curves      representing     titra- 

tions,  274 

determination  of  carbon,  295 
chromium,  280,  283,  289 
manganese,  285 
vanadium,  289 
Electromotive  force,  264 
Electron    theory,    applied    to    the 
transference  of  electricity, 
267 

Elements,  grouping  of,  3 
Emery   paper   for   polishing    metal 

surfaces,  339,  448 

polishing  powders,  341,  448 

Energy,     intensity     and     capacity 

factors,  264 
Equi-axed  grains,  464 
Equilibrium     diagram     of     copper- 
nickel  alloys,  354 
silver  alloys,  352 
tin  alloys,  453 
zinc  alloys,  452 
lead-antimony  alloys,   349 
iron-carbon  alloys,  356 
Equivalent    percentage    of    carbon 

according  to    Cain,   296 
Ergs,  relation  to  joules,  265 
Eschka's  ignition  mixture,  125,  141 
Etch-bands,  459 
figures,  363 


488 


INDEX 


Etching,  341 
dishes,  374 

method  of  Heyn  and  Bauer,  378 
of  brass  and  bronze,  448 
iron  and  steel,  358 
large  specimens,  374 
reagents        for        macroscopic 

examination,  373 
acid   mercuric   chloride  solu- 
tion, 378 
with  alcoholic  solutions  of  acids, 

358 
ammonium-cupric       chloride 

solution,  373,  380 
dilute  acid  and  alkali,  342 
ferric   chloride   solution,"  342 
Kourbatoff's  reagent,  358 
potassium-cupric    chloride 

solution,  374 
Stead's  reagent,  389 
Ether-amyl     alcohol     mixture     for 
separation    of    nickel    and 
cobalt,  227 
hydrochloric  acid  solutions,  71, 

231 
separation  for  determination  of 

aluminum,  221 
chromium,  155 
cobalt,  228 
copper,  144 
manganese,  71,  192 
sulfur,  131 
titanium,  231 
vanadium,  212 
Ether,  recovery  of,  76 
Eutectic  alloy,  347 
line,  349 

point  and  temperature,  348 
ternary,  420 
Eutectoid,  355 

Evolution  methods  for  determining 
sulfur,  133,  137 


Fahy,  F.  P.,  441 

Fales  and  Vosburgh,  Planck's  for- 
mula, 292 


Farad  or  Faraday,  electrochemical 

equivalent,  265 
Fay,    Henry,   copper  oxide  eutectic 

in  copper,  457 
effect     of     nitrogen     in     steel, 

243 

sorbite,  pearlite  and  temper  car- 
bon, 361 
Federhen,  microstructure  of  Babbitt 

metal,  477 

Ferric  alum  solution  for  determina- 
tion of  phosphorus,   109 
chloride     solution,     effect     on 
barium  sulfate  precipita- 
tion, 128,  129 
etching  with,  342,  449 
for  titanium  titration,  232 
Ferrite,  358,  362,  363,  404 
Ferro-chrome,      determination      of 

manganese  in,  85 
silicon  in,  125 
sulfur  in,  141 
manganese,     determination    of 

manganese  in,  53 
phosphorus,    determination    of 

phosphorus  in,  109 
determination  of   manganese 

in,  53 

silicon,  determination  of   phos- 
phorus in,  109 
determination  of  phosphorus 

in,  110 
determination    of   silicon    in, 

125 
determination    of    sulfur    in, 

141 

titanium,    determination  of  ti- 
tanium in,  239 
tungsten,       determination       of 

manganese  in,  85 
determination   of  oxygen  in, 

252 
determination   of   silicon    in, 

125 
determination  of  tungsten  in, 

204 
vanadium,  analysis  of,  212 


INDEX 


489 


Ferrous  sulfate  solution,  for  carbon 

determination,  33 
chromium     determination, 

151,  152,  158,  280 
manganese    determination, 

51,  57 
vanadium     determination, 

288 
Fevert,  absorption  tube  for  carbon 

dioxide,  20 

Fibrous  structure,  459 
Field,     H.     E.,    argument    against 

chemical  control,  478 
Filters,     ashless     or    washed     with 

hydrofluoric  acid,  116 
fitting  to  a  funnel,  117 
for   carbon   determination,    16, 

18,  34,  45 

paper  pulp,  116,  196 
size  of,  117 

Filtration,  rate  of,  116 
Fine-grained  structure  of  steel,  391 
Finishing  temperature,  393 
Finkener,    determination    of    phos- 
phorus in  steel,  92 
generator  for  hydrogen,  248 
tower,  116 

Flaws,  caused  by  oxide  inclusions,  4 
Fleming    bulb    for    absorption    of 

carbon  dioxide,  20 
Fletcher  burner,  use  of,  121 
Forbes,  G.  S.  and  Bartlett,  E.  P., 
electrometric        titrations, 
274,  292 

Ford- Williams  method  for  determin- 
ing manganese,  56 
Forged  material,  sampling  of,  428 
Forge-scale,  prevention  of,  426 
Forging,  effects  of,  386,  392 
Fractured  casting,  418 
Frary   electrolysis   apparatus,    145, 

179 
Fredenhagen,    theory    of    oxidation 

cells,  292 

Friedheim,  Meyer  and  Euler,  deter- 
mination of  molybdenum, 
191 


Friedrich  and  Leroux,  copper-silver 

alloys,  352 
Furnaces  for   carbon   combustions, 

11,  33,  37 


Galvanometer      for       electrometric 

titrations,  278 
Gas  retort,  analysis  of,  409 
Gauze    electrodes,    advantages     of, 

145,  179,  325 
dimensions  of,  323 
Gay-Lussac  method  for  standardiz- 
ing acid,  14 
Geissler    bulb    for    absorption     of 

carbon  dioxide,  10,  33 
"Gel"  form  of  colloids,  115 
Geryh  pump  for  oxygen  determina- 
tion, 253 
Globules  and  nodules  on  cast  iron, 

401 

Glossy  photographic  papers,  344 
Gold,  temperature  at  melting  point 
correct   for   carbon   deter- 
minations,   302 

Gooch,  F.  A.  and  Gilbert,  precipi- 
tation of  vanadium,   217 
and     Stockney     reduction     of 

vanadic  acid,  212 
crucibles,  80 

asbestos  for,  80 

Goutal,  cyanide  method  for  deter- 
mining nickel,  182 
Grain  size  of  brass  and  bronze,  462, 

464,  466 

steel,  391,  392,  393 
Grains,  equiaxed,  464 
Graphite,  7,  358 

content  of  gray  cast  iron,  412 
and  transverse  strength,  413 
influenced  by  size  of  bar,  413, 

414,  416 

rate  of  cooling,  410 
determination  of,  44 
primary  separation  of,  364 
Graphitic  temper  carbon,  7,  44,  358, 
364 


490 


INDEX 


Gray  cast  iron,  399,  410 

analysis  of,  411,  412 
disintegration  of,  421 
effect  of  remelting,  418 
inequalities  in  the  chemical 

composition,  439 
powder,  analysis  of,  438 
sampling  of,  436 
surface  separations  on,  420 
spiegel,  405 

Grossman,     cyanide     method     for 
determining  nickel,  182 

Groups  of  elements,  3 

Guertler    and    Tammann,    copper- 
nickel  alloys,  354 

Gulliver,  metallic  alloys,  338 

H 

Handy,     J.     O.,     determination   of 

phosphorus  in  steel,  94 
Hardness  of  steel  produced  by  strain, 

394 
Hasselbalch,  electrometric  analysis, 

292 
Hawes,    M.    C.,    determination   of 

tungsten,  196 
Head  of  water  compared  to  voltage, 

264 
Heat,  effect  on  physical  composition 

of  white  iron,  404 
Heating     unit     for     electrometric 

apparatus,  278 
Heycock  and  Neville,  copper-silver 

alloys,  352 
Heyn,  E.,  analysis  of  gray  cast  iron, 

412 
and  Bauer,  O.,  etching  test  for 

sulfur,  378 
etching  reagent,  373 
intercept  method  for  counting 

grains,  465 
High  temperatures,  measurement  of, 

425 
Hildebrand,    J.    H.,    apparatus   for 

electrometric  titration,  272 
curves     obtained     by     electro- 
metric  titration,  274 


Hildebrand,  J.  H.,  use  of  the  hydro- 
gen electrode,  292 
Hillebrand,    W.    F.,    separation    of 

rare  earths,  262 

Hinrichsen,  determination  of  phos- 
phorus in  steels  containing 
tungsten,  111 
determination    of    titanium   in 

steel,  231 

tungsten  in  steel,  202 
Holliday,    J.    A.,    determination    of 

tungsten,  196 

Holverscheit,  iodometric  determina- 
tion of  vanadium,  213 
Homerberg,      Victor,      photomicro- 
graphs, 359,  360,  362,  363, 
368,    370,    392,    393,    394, 
451,  454,  472,  474 
Hoop  iron,  segregation  in,  388 
Hoskins  low-voltage  electric  furnace, 

300 

Hostetter,  J.  C.  and  Roberts,  H.  S., 

electrometric  analysis,  293 

Humfrey,  J.  C.  W.,  macro  etching 

and  printing,  380 
Hundeshagen,      determination      of 

phosphorus,  92,  94 
Hydrobromic      acid      method      for 
determination      of      phos- 
phorus in  steel,  110 
Hydrochloric  acid,  arsenic  in,  318 
for     carbon     determination, 

13 
chromium     determination, 

150 

etching,  358 
nickel  determination,   176, 

186 

silicon   determination,   120 
sulfur  determination,  136 
six-normal,  136,  244 
standardization  of,  14 
electrometric  titration  curve 

of,  274 
Hydrofluoric  acid,  use  of,  53,  73,  97, 

100,  109,  118 
testing  the  purity  of,   118 


INDEX 


491 


Hydrogen    electrode,    potential    of, 

272 

ion  concentration,  271 
peroxide  for  etching,  449 

Hydroxyl  ion  concentration,  271 

Hyper-eutectoid  steel,  7 

Hypo-eutectoid  steel,  7 

Hypovanadic  acid,  206 


I 


Ice-salt  freezing  mixture,  348 

Ignited  asbestos,  34,  45 

Ignition     mixtures,     Rothe's     and 

Eschka's,  85,  125,  141 
Illuminator  for  microscopic  work  in 

the  metals,  342 
Imperial      Standard     photographic 

plates,  344 

Inequalities  in  gray  iron,  439 
Ingento  polishing  compound,  346 
Intercept  method  of  counting  grains, 

465 
lodate  solution,  134 

in  potassium  iodide,  156,  161 
Iodine  solution,  134 

for    standardization    of  thio- 

sulfate,  156 

lodometric    determination   of   anti- 
mony, 316 
arsenic,  318 
chromium,  161 
copper,  146,  327 
iron,  170 
sulfur,  133,  135 
vanadium,  212 
Ionic  reactions,  189 
lonization  of  water,  271 
Iron,  allotropic  forms  of,  354 

and    steel    metallographic    ex- 
amination of,  399 
carbide  or  cementite,  7,  357 
carbon     equilibrium     diagram, 

356 

determination  by  Mohr's  iodo- 
metric  method,  170 


Iron,  determination  by  Zimmerman- 
Reinhardt  titration,  172, 
232,  329 

in  impure  titanium  oxide,  238 
in  insoluble  materials,  173 
in  non-ferrous  alloys,  329 

phosphide,  determination  of 
phosphorus  in,  109 

removal  as  ferric  chloride  by 
ether  extraction,  71 

rust,  effect  neutralized  by  stan- 
nous  chloride,  137 

sampling  of,  423 

separation  from  manganese  by 
basic  acetate  method,  78, 
83 

silicide,  reaction  with  hydro- 
chloric acid,  115 

solidification  or  freezing  point, 
371 

white,  gray  or  mottled,  399 

wire,  standardization  of  per- 
manganate solution,  106 

wrought,  357 


Jarvis,  cyanide  method  for  determin- 
ing nickel,  182 
Jeffries,  Zay,  counting  grains,  464, 

466 
Johnson,  burned  steel,  391 

and      Jermain,      structure      of 

Muntz  metal,  455 
determination    of    phosphorus, 

100 

tungsten,  195 
Jones  reductor,  105,  194 
Jorgensen,   determination   of   phos- 
phorus, 112 
Joule,  unit  of  power,  265 

K 

Kelley,  G.  L.,  and  others,  electro- 
metric  apparatus  and 
methods,  276,  280,  285, 289, 
293 


492 


INDEX 


Kleinschmidt,  A.,  formula  of  meta- 

stannic  acid,  308 
Kilowatt-hour  and  -year,  265 
Klopsteg,  P.  E.,  electrometric  titra- 

tion  of  acid  and  alkali,  293 
Kourbatoff's    reagent,  358,  363 
Krug  method  for  determining  sulfur 

in  steel,  131 
Kiister  and  Thiel,   precipitation  of 

barium  sulfate,  128 


Ladle  test,  427 

Lady  cloth,  for  polishing,  340 
Layer  formation  in  defective  con- 
denser tube,  470 

Lead-antimony  cooling  curves  and 
equilibrium  diagram,  348, 
349 

eutectic,  474 
determination  as  chromate,  328 

sulfate,  327 

by  molybdate  titration,  315 
in  bearing  metals,  313 

brass  and  bronze,  323 
dioxide,      dissolving     off      the 

electrode,  327 

electrolytic  determination,  323 
Ledebur,     method   for   determining 

graphite,  44 
oxygen,  248 
separations   on  the   surface  of 

cast  iron,  402 
Ledeburite,  358,  364,  366 
Levigated  alumina,  338 
Lewis,      Brighton     and      Sebastian 
hydrogen       and       calomel 
electrodes,  293 

Local    differences    in    the    chemical 
composition    of    iron    and 
steel,  439 
Loomis  and  Acree,  studies  with  the 

hydrogen  electrode,  293 
Loomis,  N.  E.,  potential  of  calomel 
and  hydrogen  electrode,  293 
Loomis  and  Knowles,  determination 
of  zirconium,  258 


M 


McClendon,   J.   F.,  hydrogen  elec- 
trode, 293 

Machine  polishing,  340 
Macroscopic   examination   of   brass 

and  bronze,  448 
steel,  373 

with  aid  of  printer's  ink,  378 
Magnesia  mixture,  solution,  93,  103, 

112 

for  ignitions,  125,  141 
Magnesium  basic  chloride,  reaction 

with  silica,  126 
Magnetic  analysis,  441,  442,  443 

permeability  curves,  443 
Magnifications   and   standards   and 
methods  of  expressing,  342, 
448,  462 

Malleable  iron,  404,  406,  408 
Manby,     determination     of     phos- 
phorus in  steel,  94 
Manganese  bronze,  307 

colorimetric  determination,  70 
content  of  cast  iron  changed  by 

remelting,  403 
spiegel,  404 
determination  after  the  sulfur 

determination,  140 
as  oxide,  79 
as  pyrophosphate,  80 
as  sulfate,  82 
by   bismuthate    method,    49, 

53,  330 

by  Ford- Williams  method,  56 
by     persulfatemethod,       69, 

329 

by  Volhard  method,  59,  65 
in  alloys  rich  in  manganese, 

53,  83 
in  materials  insoluble  in  acid, 

85 

in  filtrate  from  silicon  deter- 
mination, 119 
in  non-ferrous  alloys,  329 
electrometric        determination, 
280,  283,  285 


INDEX 


493 


Manganese  bronze,  gravimetric  de- 
termination,  70,  88 
segregation,  376,  383,  387 
separation      from      chromium, 
phosphorus  and  aluminium, 
76 

iron,  71,  73,  78,  83 
sulfate  reagent,  212,  233 
Martensite,   7,  357,  359,  360,  366, 

390,  392,  404 

Maxwell,    L.    C.    and    Cain,    J.    R. 

determination  of  carbon,  11 

Mechanical    treatment,    effects    of, 

386,  392 
Mercuric  chloride  solution,  233,  473 

nitrate  solution,  473 
Mercurous    nitrate    solution,     159, 

285,  286 
Metallographic  constituents  of  iron 

and  steel,  347 
Metastannic  acid,  308,  320 
Methyl  Orange,  indicator  solution, 

14 
Meyer     bulb,     for     absorption     of 

carbonic  dioxide,  13 
Michaelis,  L.,  electrometric  titration, 

294 
Miscroscope  for  examination  of  large 

areas,  343 
general    metallographic    work, 

342 

study  of  steel,  390 
Midvale  absorption  tubes  for  carbon 

dioxide,  20 

Milli-ampere  and  milli-volt,  265 
Mixed  crystals,  see  Solid  Solution 
Mine  rail,  segregation  of  phosphorus 

in,  388 

Mohr's  iodometric  method  for  deter- 
mining iron,  170 
Molten  metal,  sampling  of,  427 
Molybdate    methods  for  lead,    315 
for   phosphorus,    91,  94,   96, 

100,  104,  109,  111 
vanadium,  209 

solution,     preparation    of,     93, 
100,  209,  315 


Molybdenum  compounds,  189 

determination  by   Blair  ether- 
extraction  method,  192 
of  oxides  in,  252 
permanganate  titration,  193 
sodium       peroxide       fusion 

method,  190 

occurrence  in  iron  and  steel,  188 
oxides  of,  188 
separation  from  arsenic,  192 

silicon,  phosphorus,  tung- 
sten, etc.  191 

Moore,   cyanide  method  for  deter- 
mining nickel,  182 
Morrell,  determination  of  sulfur  in 

steel,  128 
Motor  and  stirrer  for  electrometrie 

work,  279 
Mottled  iron,  422 
Mounting     card     for     microphoto- 

graphs,  345 
Miiller    analysis    of    remelted    cast 

iron,  403 
and    Diefenthaler,    analysis    of 

ferrovanadium,  212 
Munroe  crucible,  81 
Muntz  metal,  455,  464,  465,  468,  472 

N 

Naval  brass,  473 

Nernst  formula  for  electrolysis,  268, 

269 
Nesbitt,  modification  of  bismuthate 

method,  54 
Nessler's  reagent,  244 
Neumann,  B.,  potential  of  hydrogen 

and  metals,  294 

Nickel,  determination  after  the  de- 
termination of  sulfur,  140 
by  dimethyl  glyoxime,   175 
by  electrolytic  deposition,  178 
by  potassium  cyanide  titra- 
tion, 182,  185,  186 
in  non-ferrous  alloys,  330 
in  removal  of  silicon,  119 
plate,  estimating  the  thickness 
of,  178 


494 


INDEX 


Nitric  acid  and  alcohol  for  etching, 

358 
for  etching  brass  and  bronze, 

448 

reagent  for  bismuthate  deter- 
mination, 50,  283 
chromium  determination, 

152 

nickel   determination,    187 
phosphorus  determination, 

92,  95 
vanadium     determination, 

208 

Williams  method,  57 
standard  solution  of,  95 
Nitrides  of  iron,  243 
Nitrogen  in  steel,  determination  of, 

243,  246 

Nitrosulfuric  acid  for  silicon  deter- 
mination, 120 

Nodules  and  globules  on  iron,  401 
Nomenclature,  duolistic,  188 
Nomograph  scale,  296 
chart,  299 
scale,  296 
Non-ferrous  alloys,  307 

-metallic  inclusions  in  wrought 
iron,  368,  369 


O 


Occlusion  by  barium  sulfate,  129 
O'Daly,  section  of  Mimtz  metal,  465 
Ohm,  G.  S.,  264 
Ohm,  unit   of    electrical    resistance, 

265 

Ohm's  law,  264,  265 
Ordnance      Department     test     for 

season  cracking,  473 
Osmondite,  363 
Ostwald,  W.,  absolute  potential  of 

metals,  294 
Overheated  and  burned  steel,  391, 

392 

Oxides,  cause  of  flaws  in  steel,  4 
Oxygen,  determination  of,  248,  252 


Paper    for    printing    photo    micro- 
graphs, 344 

Pearlite,  7,  358,  361,  363,  399 
Peptonization      of      colloids,      309, 

320 
Perhydrol  or  concentrated  hydrogen 

peroxide,  66 

Permanganate    methods   for    deter- 
mining antimony,  316 
chromium,  151 
iron,  72,  232,  329 
manganese,  49,  54,  56,  59, 

69 

molybdenum,  193 
phosphorus,   104,   105,   109 
vanadium,  208,  209,  211 
solution,    50,   57,    61,    92,    105, 

152,  158,  208,  209 
addition    of    potassium    hy- 
droxide to,  61 
for  oxidation  of  phosphorus, 

92 

stability  of,  57,  62 
standardization    of,    50,    58, 

62,  106 
Persulfate    for    etching    brass    and 

bronze,  449 

method  for  determining  manga- 
nese, 69,  287 
Peters,  R.,  oxidation  and  reduction 

cells,  294 

Pettenkofer,        use        of        barium 
hydroxide     for     absorbing 
carbon  dioxide,  11 
Phenolphthalein  indicator  solution, 

95 

Phosphor  bronze,  307,  457 
Phosphorus,  90 

'   determination     as     magnesium 

pyrophosphate,  91,  101 
by  alkalimetric  method,  94 
by  basic  acetate  method,  101 
by  ferric  alum  method,  109 
by  gravimetric  methods,  91, 
97,  101 


INDEX 


495 


Phosphorus       determination       by 
method  of  C.  M.  Johnson, 
100 
by       molybdate-m  a  g  n  e  s  i  a 

method,  91 
by   molybdate    methods,  91, 

94,  96,  100,  104,  109,  111 
by  volumetric  methods,  94, 

96,  100,  104,  109 
in  alloy  steel,  109 
in  cast  iron,  96 
in  ferrosilicon,  109 
in  iron  containing  titanium, 

97 

in  iron  phosphide,  109 
in        materials       containing 

arsenic,  110 
insoluble  in  acid,  109 
soluble  in  acid  91,  94,  100, 

101,  104 

in  non-ferrous  alloys,  330 
in  steel  containing  tungsten, 

111 

vanadium,  101,  114 
effect  on  zirconium  determina- 
tion, 262 

in  wrought  iron,  434 
segregation  of,   369,   376,    383, 
384,    385,    387,    388,    430, 
431,  432 
separation  from   molybdenum, 

191 
Photographing  polished  and  etched 

specimens,  343 
Photomicrographs,  camera  for,  342 

mounting  card  for,  345 
Picric  acid  solution  for  etching,  358 
Planck,  M.,  potential  differences,  294 
Planing  the  sample,  423,  424 

versus  boring,  369,  387 
Plastic  bronze  lead  in,  451 
Plates  for  photographic  work,  343 
Platinum  tubes  for  combustion  of 

steel,  12 

crucibles,    tubulated    for   com- 
bustions, 11 
electrodes,  145,  323,  327 


Platz,     analysis    of    globules     and 

nodules  on  cast  iron,  402 
"Policeman"  use  of,  117 
Polished  specimens,  photographing, 

343 

preparation  of,  338 
Polishing,  direction  of,  339,  448 
compound,  346,  448 
surface  flow  during,  340 
the  specimen,  338 
wheel,  340 

with  suspended  abrasives,  341 
Porcelain  combustion  tubes,  12,  33, 

40 
Potassium  acid  tartrate  fusion  with, 

164,  214 
chloride        solution,        electric 

resistivity  of,  305 
cupric  chloride  solution,  9,  32, 

34 

cyanide  solution,  183,  186 
methods  for  determining 

nickel,  182,  185,  186 
dichromate     for     electrometric 

methods,  280,  288 
ferricyanide  indicator,  152 
ferrocyanide  method  for  titrat- 
ing zinc,  331 
hydroxide    for    absorption    of 

carbon  dioxide,  9 
iodate  method  for  determining 

copper,  317 
solution,  136 
iodide  solution,  184,  186 
nitrate  solution,  94 
permanganate       method       for 
determining  antimony, 
316 

chromium,  152 
iron,  72,  232,  329 
manganese,   49,   54,   56, 

59,  69 

molybdenum,  193 
phosphorus,  104,  105,109 
vanadium,  208,  209,  211 
solution,  50,  57,  61,  92,  105, 
152,  158,  208,  209 


496 


INDEX 


Potassium,  permanganate  method  for 
determining  antimony, 
solution,  addition  of 
potassium  hydroxide 
to,  61 

for    oxidation    of    phos- 
phorus, 92 
stability  of,  57,  62 
standardization    of,    50,    58, 

67,  106 
pyrosulphate,     fusion    with, 

234,  258,  261 
titanium  fluoride,  235 
Potential     of     normal     and     other 

electrodes,  272,  273 
differences,  264 
Power,  measurement  of,  265 
Precipitates,  handling  of ,  117 
Preparation  of  specimens  for  metal- 
lographic  examination,  337, 
446 

Pressing  steel,  effect  of,  392 
Printer's   ink   for    macroscopic    ex- 
amination    of     specimens, 
378 
Printing  on  silk  as  a  test  for  sulfides, 

376 

Process  plates,  344 
Puddled  iron,  433 
Pulverizing  hard  materials,  426 
Pyrosulfate  of  potassium,  234 


Quenching,  effect  of,  355 


R 


Rare  earths,  262 

Rate  of  cooling,  influence  on  forma- 
tion of  graphite,  410 

Red-short  boiler  plate,  388 

Reinhardt,  C.,  chemical  composition 
of  gray  iron,  439 

Remelting,  effect  on  chemical  com- 
position of  cast  iron,  403, 
418 


Resistivity,  electrical,  264 

of    barium    hydroxide    solu- 
tions, 296,  298 
potassium  chloride  solution, 

305 
Richter,  determination  of  carbon  in 

steel,  8 

Roberts,  H.  S.,  electro  metric  appa- 
ratus, 275,  294 
and     Hostetter,     electrometric 

titrations  of,  275 

Robinson,  C.  S.,  and  Winter,  O.  B., 
electrometric    titration    of 
arsenical,  275,  294 
Rolled  materials,  sampling  of,  428 
Rolling,  effects  of,  386,  392 
Rosenhain,    amorphous    cementing 

material,  468 
physical  metallurgy,  338 
slip-bands  in  strained  materials, 

458,  459 

Rosenheim       and       Holverscheidt, 
reduction  of  vanadic  acid, 
212 
Huldinsky       precipitation       of 

vanadium,  217 

Rothe  ignition  mixture,  85,  125,  216 
method   for   removal   of   ferric 

chloride  by  ether,  71 
arsenic     by     hydrobromic 

acid,  111 

shaking  funnel,  71 
Rouge,  338 

Rust,  determination  in  borings,  252 
effect  on  sulfur   determination, 
137 


S 


Salt  bridge  in  electrolysis,  271 

solution,  137 

Samples,  annealing  of,  425 
Sampling,  from  molten  metal,  427 

in  special  cases,  440 

methods  of  U.  S.  Steel  Corp,, 
427 

of  gray  iron,  436 


INDEX 


497 


Sampling,  hard  materials  which  can- 
not be  machined,  426 
iron  and  steel,  423 
pig  iron,  435 
powdered  cast  iron,  438 
rolled   and  forged  materials, 

428 

white  iron,  435 
wires,  427 
wrought  iron,  432 
Sawyer,  bismuth-tin  alloy,  350 
Schmidt    and    Hoagland,     electro- 
metric   measurements  and 
bibliography,  294 
Screen  for  use  with  colored  alloys, 

344 

Season  cracking,  470,  473 
Segregation  in  a  connecting  rod,  32, 

385 

screw,  383 

a  malleable  casting,  408 
a  mine  rail,  388 
an  I-beam,  382,  386 
basic-Bessemer  steel,  375,  382, 

385 
boiler-plate,  431,  432 

of     carbon,     silicon    aad 
phosphorus  in  spiegel, 

404 

of    phosphorus    and  sul- 
phur,  430 
stripes,  430 

Self-hardened  steel,  sampling  of,  426 
Selvyt  for  polishing  cloth,  340 
Sharp  and  Hoagland,  use  of  hydro- 
gen, electrode,  294 
Shavings  of  metal,  collection  of,  424 
Sheet  iron,  sampling  of,  388 
Shepard,     copper-zinc     equilibrium 

diagram,  452 
Shimer,    P.    W.,    determination  of 

phosphorus  in  steel,  104 
Sieves,  437 
Silica,  recovery  of  aluminum  from, 

220 

titanium  from,  233 
tungsten  from,  199 

32 


Silica,  recovery  of  zirconium  from, 

258 

testing  the  purity  of,  118 
Silicic  acid,  colloidal,  115 

dehydration  of,  116,  119 
Silicide  of  iron,  reaction  with  hydro- 
chloric acid,  115 
Silico-manganese,   determination  of 

manganese  in,  85 

Silicon,  blank  determination  of,  120 
content    of    iron    changed    by 

remelting,  403 

determination  accuracy  of,  122 
by  Drown  method,  119 
solution     in     hydrochloric 
acid,  115 

nitric  acid,  121 
in  alloys  and  metals,  124,  127 
in  cast  iron.  120,  122 
ferro-silicon,    ferro-chrome 

and  ferro-tungsten,  125 
materials  insoluble  in  acid, 

124 
presence  of  tungsten,  117, 

118,  122 
titanium,  127 
molybdenum,  191 
soluble  materials,  115 
dioxide,  see  Silica 
metallic,  treatment  of,  125 
rapid  method  of  removing,  88 
reaction  with  fused  sodium  car- 
bonate, 124 

segregation  in  boiler  pla^te,  432 
volatilization    as    tetrafluoride, 

118 

Silver  nitrate  solution  for  electro- 
metric     determination 
of  chromium,  280 
potassium  cyanide  titra- 

tions,  184 
Size  of  grains  in  metals,  462,  464, 

466 

rods  and  effects  on  strength 
and  on  graphite  formation, 
413,  416 
Slag  areas  in  brass,  457 


498 


INDEX 


Slip  bands  in  strained  material,  458, 

459 

Soda-lime  tubes,  25,  26 
Sodium  arsenite  solutions,  51,  62, 

67 
bismuthate  methods,  49, 53, 54, 

154,  283,  285,  330 
bisulfite  solution,  208 
carbonate  solution,  55 

and  acetate,  fusion  with,  164 
chloride  solution,  137 
chromate    solution    as    colori- 

metric  standard,  150 
hydroxide,  standard  solution  of, 

14,  95,  244 

oxalate  as  a  standard  for  volu- 
metric analysis,  50,  58,  62 
peroxide  fusion,    76,    165,    190, 

202,  216 
thiosulfate    solution,    63,    134, 

147,  232 
standardization  of,  63,  147, 

156 

"Sol"  form  of  colloids,  115 
Solder,  464 
Solid  solution,  351 

of  iron  carbide  in  iron,  7 

zinc  in  copper,  454 
Solution  pressure,  266 
Sorbite,  7,  358,  361,  392 
Sorensen,  S.  P.  L.,  concentration  of 

hydrogen  ions,  294 
Specimens,   preparation  and  treat- 
ment of,  337,  446 
Spheroidized  cementite,  362 
Spiegel,  analysis  of,  404 
effect  of  remelting,  403 
white  and  gray,  405 
Split  mold,  use  of,  427 
Spongy  electrolytic  deposits,  325 
Standard  magnifications,  342,  462 

orthonon  plates,  343 
Standardization  of  acid  and  alkali, 

14 

permanganate,  50,  58,  62,  106 
sodium  thiosulfate,  63,  147,  156 
Stannic  hydroxide,  308 


Starch  solution,  136,  157 
Stead,  etching  reagent,  389,  392 
Steel,  cast,  369 

chemical     and     metallographic 
study  of  the  solid  ingot,  371 
decarbonization  of,  396 
fine-grained  structure,  391 
general   microscopic    study   of, 

390 

macroscopic  examination  of,  373 
metallographic     characteristics 

of,  370 

over-heated  and  burned,  391 
sampling  of,  423 
segregation  during  cooling,  371 
Stetzer     and     Norton     combustion 

train,  20 
Stirrer  and  motor  for  electro  metric 

titrations,  279 

Strain  hardness  of  steel,  394 
Sudden  cooling  of  an  alloy,  355 
Sulfides,  test  for,  378 
Sulfur,  applicability  of  methods  for 

determining,  140 
blank  determination,  139 
colorimetric  determination,  129 
determination     by     Bamber 

method,  131 
absorption  in  bromine  and 

acid,  129 

ether  method  of  Krug,  131 
evolution     methods,      129, 

133,  137 
in  ferrochrome  and  ferro-silicon, 

141 

insoluble  materials,  141 
iodometric  methods,  133, 135 

presence  of  iron,  130 
effect    of    rust    on    evolution 

method,  137 
ferric    ions   on    precipitation 

methods,  128,  129 
occurrence  in  iron  and  steel,  128 
prints,  376,  379,  429 
red-shortness  due  to,  388 
segregation  of,   384,   385,   387, 
388,  430,  431 


INDEX 


499 


Sulfuric  acid,  effect  of  ferric  salt  on 
its  precipitation,  128,  129 
for  chromium  determination, 

152,  280,  283 

copper  determination,  144 
phosphorus  determination, 

105 
from  atmosphere  and  reagents, 

131,  139 

Surface  flow  of  metal  during  polish- 
ing, 340 
separations  on  white  iron,  402 


Tabary,  O.,  analysis  of  gray  iron, 

440 

Tague,  E.  L.,  use  of  hydrogen  elec- 
trode, 294 

Tartaric  acid  solution,  176 
Tart  rate    fusion    mixture,    for    use 
in  determining  chromium, 
164 

Temper  carbon,  7,  44,  361,  365 
Temperature  coefficient  of  resistiv- 
ity   of    barium    hydroxide 
solution,  298 
indicated   by   color   of    heated 

metal,  425 
measurement  of,  425 
of  electric  furnace  for  carbon 

combustions,  302 
Tempering  steel,  390 
accidental,  409 
Ternary  eutectic,  420 
Test  pieces,  cleaning  of,  424 
polishing  of,  339,  448 
Thickness    of    iron,    influence     on 

graphite  formation,  414 
Thiosulfate  solution,  preparation  of, 

134,  147,  156 
reaction  with  iodine,  157 
standardization   of   63,    147, 

156 
Thorium,     effect     in     determining 

zirconium,  262 

Thumb-print  structure  of  eutectics, 
355 


Tin-antimony  alloys,  474 

compound  in  alloys,  476 
-copper    compound    in    alloys, 

47 

equilibrium  diagram,  453 
determination  in  bearing  metal, 

313 

brass  and  bronze,  321 
iodo metric   determination,   316 
rapid    gravimetric    determina- 
tion, 322 

reaction  with  nitric  acid,  308 
Titanium,  231 

alloys,  analysis  of,  127,  239 
colorimetric  determination,  234 
determination      in      difficultly 

soluble  material,  239 
presence  of  zirconium,  261 
oxide,    determination    of 

iron  in,  238 
separation  from  iron  by  ether, 

231 

standard  solution  of,  235 
volumetric     determination    of, 

236 
Titration   curves   obtained   electro- 

metrically,  274 

Toepler  pump  for  use  in  the  deter- 
mination of  oxygen,   255 
Total  carbon,  determination  in  iron 

and  steel,  8 
Train  for  combustion,    12,   20,  24, 

33,  40 
Transverse   strength   of   cast   iron, 

413 

Troostite,  7,  357,  360,  392 
Tschugaeff ,  dimethylglyoxime 
reaction    with    nickel,    175 
Tubulated  crucible  for  combustions, 

11 
Tungsten,  195 

analysis  of  the  metal,  204 
determination  as  trioxide,  195, 

197 

in    difficultly    soluble  mate- 
rials, 204 
of  oxygen  in,  252  • 


500 


INDEX 


Tungsten,  effect  on  determination  of 

silicon,  117,  118,  122 
zirconium,  262 

separation  from  iron  by  fusion 
with  sodium  peroxide, 
202 

molybdenum,  191,  194 
other  metals  elements,  199 
steels,   determination  of  phos- 
phorus in,  109,  111 
trioxide,     see     Tungstic     Acid 

Anhydride 
Tungstic  acid  anhydride,  195 

purification  of,  199,  201 
volatility  of,  118,  196 
Twinning  of  crystals,  461,  464 


U 


Uranium,  effect  on  determination  of 

zirconium,  262 
Urea,   use   in   electrolysis   of  nitric 

acid  solutions,  325 


Vacuum  furnace  for  determination  of 

oxygen,  252 
Valve,  Bunsen  and  Contat-Gockel, 

237 
Vanadic  acid,  206 

reduction  of,  212 
Vanadium,  206 

characteristic  reactions  of,  207 
after  a  fusion,  216 
after  the  determination  of 

sulfur,  140 
determination  by  Blair  method, 

210 

•  ether  method,  212 
gravimetric  method,  217 
iodometric  method,  212 
permanganate  method,  211 
phosphomolybdate  precipi- 
tation, 208 

electro  metric  determination  of, 
288,  289 


Vanadium,  effect  on  chromium  de- 
termination, 160 
on    electro  metric    determina- 
tion of  chromium,  283 
on  phosphorus  determination, 

101,  109,  113,  122 
on  silicon  determination,  122 
on  zirconium  determination, 

262 

oxides  of,  206,  207 
precipitation      as      ammonium 

metavanadate,  217 
rapid      routine      method      for 

determining,  210 
reduction  from  the  quinqueVa- 

lent  state,  212 
results  of  test  analyses,  218 
separation  from  chromium,  211 

molybdenum,  191 
Vanier  combustion  train,  20 
Velox  paper  for  sulfur  prints,  378 
Vertical  illuminator,  342 
V.    Bichowsky,   electrometric  titra- 

tion  of  zinc,  294 
Vogel's  test  for  cobalt,  227 
Volhard    method    for    determining 

manganese,  59 
Voltage  series,  267 
Volts,  264,  265 
Von  Reis,  arsenic  in  iron  and  steel, 

224 

Von  Suchtelen  and  Itano,  electro- 
metric  titrations,  294 

W 

Walker-Patrick   method  for   deter- 
mining oxygen,  252 

Walpole,  G.  S.,  gas  electrodes  and 
hydrogen  potential,  294 

Water  free  from  ammonia  and  am- 
monium salt,  244 
ionization  of,  274 

Watt-second  and  watt-hour,  265 

Wedge  formation  in  boiler  plate,  431 

Weighing,  accuracy  of,  27 

the  solution  in  order  to  obtain 
an  aliquot  part,  84 


INDEX 


501 


Wellington    ortho     process    plates, 

343 

Wet  combustion  of  steel,  23 
White  bearing  metal,  474 
iron,  399 

effect  of  annealing,  404 
heat  on  physical  composi- 
tion, 404 

gas  retort,  analysis  of,  409 
sampling  of,  435 
surface  separations  on,  402 
spiegel,  405 
Wiborgh,  colorimetric  determination 

of  sulfur,  129 
Williams    method    for    determining 

manganese,  56 

R.    S.,    Principles  of  Metallog- 
raphy, 338 
Wilsmore   and    Ostwald,    Electrode 

Potentials,  294 
Wires,  sampling  of,  427 
Wohler,  determination  of  carbon  in 

steel,  8 

Worked  brass  and  bronze,  458 
Wratten  M  photographic  plates,  343 
Wrought  iron,  357,  367 

etched  specimens,  434 

made    by    bushelling    scrap 

iron,  367 
sampling  of,  432 
segregation  of  phosphorus  in, 

369 
slag  in,  368,  369 


Wust,  F.,  analysis  of  a  white   iron 
retort,  409 


X-ray  examination  and  testing,  441, 
443 


'Yellow  precipitate,"  90 


Zimmermann-Reinhardt  method  for 
titrating  iron,  172,  232,  329 
Zinc    ammonium    phosphate,    solu- 
bility of,  333 
-copper    equilibrium    diagram, 

452 
determination  as  oxide,  333 

phosphate,  332 
by  ferrocyanide  titration,  331 
in  non-ferrous  alloys,  331 
electrolytic  determination,  332 
-magnesium  alloy,  237 
oxide  suspension  for  the  Vol- 
hard  determination,  66,  68 
solid  solution  in  copper,  454 
Zirconium,   determination  in  steel, 

258 

influence  of  phosphorus,  vana- 
dium, etc.,  on  its  determina- 
tion, 262 

separation  from  ceria  and 
thoria,  263 


14  DAY  USE 

RETURN  TO  DESK  FROM  WHICH  BORROWED 

LOAN  DEPT. 

This  book  is  due  on  the  last  date  stamped  below,  or 

on  the  date  to  which  renewed. 
Renewed  books  are  subject  to  immediate  recall. 


REC'D  LD 


NOV7     1956 





REC'D  LD    AU(UO'68-3PM 


APR  14 1988 


1  7 


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LD  21-100m-6,'56 
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